\part Labels and\\Cross References\endpart

\chapter The \CS{label} mechanism\label{LBL1}\endchapter

\lamstex's 
*\label* mechanism---one of its most crucial features---involves
several different parts of \lamstex@, and will occupy the next few 
chapters.
The present chapter merely explains the basic strategy, without
presenting any explicit code.
 (Section~\Sref{ATEVERY}
also explains about an important
 new  construction 
that  has  been added to \lamstex.)    


\section{Constructions that can be given \<{\rm label}\>'s\label{bl}}
For any \lamstex\ construction *\foo* that can be given a \<label\>, 
\lamstex\ uses 
\setbox0\hbox{for the counter associated with *\foo*}%
\setbox1\hbox{for the ``pre'' material associated with *\foo*}%
\setbox2\hbox{for the ``post'' material associated with *\foo*}%
\setbox3\hbox{for the style associated with *\foo*}%
\setbox4\hbox{for the numbering style associated with *\foo*}%
\setbox5\hbox{for the font associated with *\foo*}%
**
\foo@C  "box0 "8PQ"8
\foo@P  "box1
\foo@Q  "box2
\foo@S  "box3
\foo@N  "box4
\foo@F  "box5
**
So, for example, *\tag* has an associated counter *\tag@C*, 
and associated control sequences *\tag@P*
\dots, *\tag@F*;
 *\claim* has an associated counter
*\claim@C*,  and associated control sequences *\claim@P*,
\dots, *\claim@F*; etc.
 The values of the
*\...@C* counters can be manipulated directly, or indirectly 
 through *\Reset* and *\Offset*, and the *\...@P*,
*\...@Q*, *\...@S*, *\...@N*, and *\...@F* control sequences can be
redefined directly, or indirectly using
*\newpre*, \dots, *\newfontstyle*. (This is covered in detail in
Chapter~\ref{acces}.)

\medskip

Moreover, every *\tag* in a displayed formula, every *\claim...\endclaim*,
etc., locally defines
four quantities,
*\thelabel@*, \dots, *\thelabel@@@@*, to be used if the construction is
ever  given a 
\<label\>:
$$\vbox{\openup\jot
\halign{#\hfil&\ \ #\hfil\cr
 {\tt\bs thelabel\@}&will be the value of\ \ 
  {\tt\bs ref\lcurly}\<label\>{\tt\rcurly}\cr
 {\tt\bs thelabel\@\@}&will be the value of\ \ 
  {\tt\bs Ref\lcurly}\<label\>{\tt\rcurly}\cr
 {\tt\bs thelabel\@\@\@}&will be the value of\ \ 
  {\tt\bs nref\lcurly}\<label\>{\tt\rcurly}\cr
 {\tt\bs thelabel\@\@\@\@}&will be the value of\ \ 
   {\tt\bs pref\lcurly}\<label\>{\tt\rcurly}\cr}}
$$
All \lamstex\ constructions that can be given a \<label\> implicitly provide
grouping 
\footnote{*\claim...\endclaim* and all similar \lamstex\ constructions  
 provide grouping; in the case of *\tag* the grouping in question is
provided by the display *$$...$$* in which the *\tag* lies.}
and outside of the group
*\thelabel@@*, \dots, *\thelabel@@@@* are undefined (unless the
construction happens to lie
 within another construction that can be given a \<label\>).
However, we will initially 
**
\let\thelabel@=\relax
**
Then  the simple test
**
\ifx\thelabel@\relax  "8IFTL"8
**
will be true unless
 we are in a construction where *\label* is
legitimate. 

\medskip

As a (somewhat contrived)
 example of how this works,  
 suppose that in the third section of some document,  *\claim*
numbers are being printed as {\bf(3.i)}, {\bf(3.ii)}, {\bf(3.iii)}, \dots,
and that before the tenth *\claim* we state
**
\Offset\claim0
\newpost\claim{-A}
**
so that the number of the tenth *\claim* will be printed as
`{\bf(3.ix-A)}'. 
 
Then within the tenth *\claim*
$$\openup\jot\tabskip\centering
 \halign to\hsize{\hskip30pt#\hfil\tabskip0pt&\ \ #\ \ \hfil&\ #\hfil
  \tabskip\centering\cr
 \llap{the value of\ \ }{\tt\bs claim\@C}&will be&{\tt9}\cr
 \noalign{\vskip2pt}
 {\tt\bs claim\@P}&will be&{\tt3.}\cr
 {\tt\bs claim\@Q}&will be&{\tt-A}\cr
 {\tt\bs claim\@S\#1}&will be&{\tt(\#1)}\cr
 {\tt\bs claim\@N}&will be&{\tt\bs roman}\cr
 {\tt\bs claim\@F}&will be&{\tt\bs bf}\cr
 \noalign{\bigskip\hbox{and, correspondingly}\bigskip}
 {\tt\bs thelabel\@}&will be&{\tt\bs roman\lcurly9\rcurly}\cr
 {\tt\bs thelabel\@\@}&will be&{\tt (3.\bs roman\lcurly9\rcurly-A)}\cr
 {\tt\bs thelabel\@\@\@}&will be&{\tt 9}\cr
 {\tt\bs thelabel\@\@\@\@}&will be&{\tt 3.\bs roman\lcurly9\rcurly-A}\cr}
$$

The value of the counter  for *\claim*,
the numbering style, the pre- and post-material, and the style for *\claim*
are all involved in the values of *\thelabel@*, \dots, *\thelabel@@@@*;
see section~\Sref{QF} regarding the font style.


\section{Restrictions}
The first concrete example of defining
 *\thelabel@*, \dots,
*\thelabel@@@@*   
 occurs in Chapter~\ref{DF}. For the moment, we simply want to note that
these control sequences will essentially
be created using *\edef*'s, to insure that
they will
contain 
the current
values of the counter, numbering style, etc. Moreover, they will often occur
in *\xdefs*'s 
and *\write*'s (see page~\ref{GGGG}).


  This means that
\setbox0\hbox{*\...@P*}%
\setbox1\hbox{*\...@Q*}%
\setbox2\hbox{*\...@S*}%
\setbox3\hbox{*\...@N*}%
\setbox4\hbox{*\xdef*'s}%
\setbox5\hbox{*\write*'s}%
$$
\pagelabel{necc}
\boxed{\vbox{\halign{\hfil#\hfil\cr
  Any control sequences appearing in\cr 
 \box0, \ \ \box1, \ \ \box2, \ \ or \ \ \box3\cr 
must be ones that can appear in \box4 \ and \box5.\cr}}}$$
 Actually, we will use *\noexpands@*
(Chapter~\ref{noexpands}) to inhibit expansion during the
*\edef*'s,
*\xdef*'s,\pagelabel{plex} and *\write*'s 
(pages~\ref{A1}, \ref{A2}, et al.), 
 so 
the proper
 strategy is to allow only control sequences for which *\noexpands@*
prevents expansion.

\medskip
We've already noted (page~\ref{IC}) that *\let\/=\relax* was added to
the token list
*\noexpandtoks@* because *\/* often appears in *\...@S* definitions;
and *\let\rm=\relax*, \dots\ were added because font change control sequences
often appear also---see, for example,  pages~\ref{CCC} and
~\ref{tagit}.

Similarly, page~35 of the \lamstex~Manual indicates that if a new 
font selection command *\TimesRoman* is ever going to be used 
in defining the style for anything that can be labelled, then
*\Nonexpanding\TimesRoman* ought to be added,
and if a new numbering
command *\Babylonain* is ever going to be used
to number anything that can be labelled, 
 then we should add
 *\Nonexpanding\Babylonian*
to the file.
\footnote{The \lamstex~Manual also indicates that 
 the style file for that manual (and for this manual, as well) includes
*\Nonexpanding\FC*,
 because the ``font complement'' *\FC*  command
occurs in
 *\footmark@S* and *\foottext@S*.}

\section{Consequences of these restrictions}
Since constructions like *\newpre*  simply define various *\...@P*
control sequences, the restrictions of the previous section
also mean  that 
in constructions like
**
\newpre\tag{...}
**
{\it any control sequences in `*...*' must be ones for which *\noexpands@*
prevents expansion}.  And this means that some of the things stated, and
implied,
 in the  \lamstex~Manual are false.

While the illustrations of *\newpost*  given for *\tag*  and the
illustrations of  *\newstyle* and *\newnumstyle*  given in connection
with *\list* were quite legitimate,
  the small print on  page~77  gives the example
**
\newpre\exno{\value\HL1.\value\hl1.}
**
for  numbering a user-created construction.
But this example is completely
 wrong! Things like *\value* can't be  used
for  *\newpre*.  

Instead, we need something like\pagelabel{FNEPG}
\footnote{To\label{FNEP} be on the safe side, we might prefer
*\Evaluatepref\HL1 \edef\HLvalue{\Pref}*, \dots, in case 
*""...""* has been used to quote a heading level, but *\Evaluate* will
illustrate the point well enough.}
\Litbox0=**
\Evaluate\HL1 
\edef\HLvalue{\number\Value}
\Evaluate\hl1
\newpre\exno{\HLvalue.\number\Value.}
**
$$\vcenter{\box0}\tag"\style{\bf A}"\pagelabel{EXNO}$$
And the situation is even  more complicated,
because we need to restate this after every *\hl1*.


\section{\CS{Initialize}\label{ATEVERY}}
To handle such situations,
 \lamstex\ now has  the construction
*\Initialize* (the details of which are described in sections
~\Sref{HLC}
and ~\Sref{EVERY}). 
If you type
\Litbox0=**
\Initialize\hl1{\Evaluate\HL1   "8AEEX"8
 \edef\HLvalue{\number\Value}%
 \Evaulate\hl1
 \newpre\exno{\HLvalue.\number\Value.}}
**
$$\vcenter{\box0}\tag"\style{\bf B}"$$
then the set of commands ({\bf A}) will be 
executed each time an *\hl1* occurs.

Similarly,
**
\Initialize\HL1{\newpre\hl1{}}
**
would make the  pre-material for *\hl1*  be empty  even for  the default
style, which normally  makes the pre-material for *\hl1* be `*1.*' in
the first *\HL1*, and `*2.*' in the second, etc. 

  If *\chapter* and *\section* 
have been  introduced
 as names   for *\HL1* and *\hl1*  (see Chapter~\ref{HLS} for details),  
then we can substitute *\chapter* for *\HL1* and/or *\section* for
*\hl1* in the *\Initialize* command, e.g.,  
**
\Initialize\chapter{\newpre\section{}}
**


[Different *\Initialize* commands don't accumulate, so if you later want
to add *\newpre\hl2{}*, then you must use
**
\Initialize\HL1{\newpre\hl1{}\newpre\hl2{}}
**
This  shouldn't be much of a problem, since such commands are rather special,
and would probably go near the beginning of a document; moreover, if  they
did accumulate, it would quite dicey to {\it cancel\/} any such command.]

As an extra bonus, within the *\Initialize*
construction, 
*\pref* may be used with a special significance. For example,
in something like
**
\Initialize\hl1{\newpre\exno{\pref.}}
**
the `*\pref*' will give the value that *\pref* would have for a \<label\>
in the  *\hl1* that has just been executed.
 Consequently, in the default
style 
 this will have  the 
same effect
 as ({\bf B}).
\footnote{More precisely, it will have the same effect as if we had used
*\Evaluatepref*, as suggested in footnote~\ref{FNEP} on page~\ref{FNEPG}.}



\section{The  question of fonts\label{QF}}
Note that the font for *\claim* is not recorded anywhere in
*\thelabel@*, \dots, *\thelabel@@@@*---it is relevant only when the
*\claim* number is actually printed.


Thus,
as we'll see in Chapter \ref{acces},
*\Ref{*\<label\>*}* will not print `{\bf(3.ix-A)}',
but simply `(3.ix-A)' [or `{\it(3.ix-A)\/}'
 if we are using italic type, etc.].
But
we can get \hbox{`{\bf(3.ix-A)}'} by typing
*\fontstyle\claim{\Ref{*\<label\>*}}*, 
which expands out (page~\ref{FS}) to
\setbox0\hbox{\<label\>}%
**
{\claim@F\Ref{"box0}}
**
 This seems like the optimal
arrangement, giving the option of using the same font  or not.



Note, \pagelabel{SGG} by the way, that
to print *\claim* numbers
 as ({\bf3.i}), ({\bf3.ii}), ({\bf3.iii}), \dots, with bold numbers and
letters, but with
 {\it \hbox{roman}\/} parentheses, we would define *\claim@S*
(either directly, or indirectly through *\newstyle*), 
to be
**
\def\claim@S#1{{\rm(}#1\/{\rm)}} "8CCC"8
**
and *\fontstyle\claim{\Ref{*\<label\>*}}* will then give 
the claim number printed in exactly this way. (The *\/* is useful
in case *\claim@F* is ever chosen to be a slanted font.)\pagelabel{ic2}




\section{Storing \<{\rm label}\>'s}
Every time a valid *\label{*\<label\>*}* or *\pagelabel*
appears, so that \<label\>
can be given associated values *\ref{*\<label\>*}*, \dots, \lamstex\ has
to record this information in two places:
\list
\item The information must be kept internally, in a new control sequence
that we will consider in a moment.
\item The information must also be written to the auxiliary *.lax* file.
\footnote{In version *1* of \lamstex@, the auxiliary file had the
extension *.aux*; however, this has been changed to *.lax* (``\lamstex\
auxiliary file''), not only to avoid conflict with *.aux* files produced by
\latex@, but also because \lamstex\ can now
write *.aux* files also (Chapter~\ref{bibtex});
 these have the structure of \latex\ auxiliary
files, but contain only entries relevant to \bibtex@, so that
\bibtex\ can be used with \lamstex\ files also. In conformity with this
change, the old 
*\readaux* has been changed to *\readlax* (section~\Sref{rl}).}
\endlist

The reason for writing to the auxiliary file, of course, is so that the
information from that auxiliary file can be read in again the next time the
document is \tex'ed, thus allowing for forward references.

It will be important to distinguish information  read in from the
auxiliary file from  information created on the current run,
 and also to
distinguish labels created by *\label* from those created by
*\pagelabel*.




\medskip
The basic datum that we will be recording in the *.lax* file
 will be a term of
the form
\setbox0\hbox{\<label\>}\setbox1\hbox{V$_{\text1}$}\setbox2
\hbox{V$_{\text2}$}\setbox3\hbox{V$_{\text3}$}\setbox4\hbox{V$_{\text4}$}%
\setbox5\hbox{\<type indicator\>}
**
@"box0~"box1~"box2~"box3~"box4~"box5    
**
where
$$\align%at2 
 \hbox{V}_{\text1}&=%\hbox{value of {\tt\bs thelabel\@}}&&=
 \hbox{value of {\tt\bs ref\lcurly}\<label\>{\tt\rcurly}}\\
 \hbox{V}_{\text2}&=%\hbox{value of {\tt\bs thelabel\@\@}}&&=
 \hbox{value of {\tt\bs Ref\lcurly}\<label\>{\tt\rcurly}}\\
 \hbox{V}_{\text3}&=%\hbox{value of {\tt\bs thelabel\@\@\@}}&&=
 \hbox{value of {\tt\bs nref\lcurly}\<label\>{\tt\rcurly}}\\
 \hbox{V}_{\text4}&=%\hbox{value of {\tt\bs thelabel\@\@\@\@}}&&=
 \hbox{value of {\tt\bs pref\lcurly}\<label\>{\tt\rcurly}}
%\endalignat
\endalign
$$
and the \<type indicator\> is
$$
\align
 \hbox{\tt0}&\hbox{\ \ if \<label\> was created by a {\tt\bs label} on the
current run}\\
 \hbox{\tt1}&\hbox{\ \  if \<label\> was created by a {\tt\bs label} on the
 previous run}\\
\hbox{\tt2}&\hbox{\ \  if \<label\> was created by a {\tt\bs pagelabel} on the
current run}\\
 \hbox{\tt3}&\hbox{\ \ if \<label\> was created by a {\tt\bs pagelabel} on the
 previous run}\endalign$$
Each *\label{*\<label\>*}* will create a new control sequence
`*\*\<label\>*@L*' with the value
\newbox\boxx \newbox\boxxi
\setbox0\hbox{\<label\>}\setbox1\hbox{V$_{\text1}$}\setbox2
\hbox{V$_{\text2}$}\setbox3\hbox{V$_{\text3}$}\setbox4\hbox{V$_{\text4}$}%
\setbox5\hbox{\<type indicator\>}
\setbox6\hbox{\<label\>$'$}\setbox7\hbox{V$_{\text1}'$}\setbox8
\hbox{V$_{\text2}'$}\setbox9\hbox{V$_{\text3}'$}\setbox\boxx\hbox{V$_{\text4}'$}%
\setbox\boxxi\hbox{\<type indicator\>$'$}
**
"box1~"box2~"box3~"box4~"box5
**
(we use quotes around *\*\<label\>*@L* as on pages~\ref{QTS1} and~
\ref{QTS2}),\pagelabel{QTS3}
and it will also write
\newbox\boxx \newbox\boxxi
\setbox0\hbox{\<label\>}\setbox1\hbox{V$_{\text1}$}\setbox2
\hbox{V$_{\text2}$}\setbox3\hbox{V$_{\text3}$}\setbox4\hbox{V$_{\text4}$}%
\setbox5\hbox{\<type indicator\>}
\setbox6\hbox{\<label\>$'$}\setbox7\hbox{V$_{\text1}'$}\setbox8
\hbox{V$_{\text2}'$}\setbox9\hbox{V$_{\text3}'$}\setbox\boxx\hbox{V$_{\text4}'$}%
\setbox\boxxi\hbox{\<type indicator\>$'$}
**
@"box0~"box1~"box2~"box3~"box4~"box5
**
to the *.lax* file.

*@* and *~* are simply two conveniently chosen tokens that should
not appear within any \<label\>.  Actually, the *@* and *~* appearing
in the definition of `*\*\<label\>*@L*' and in the *.lax* file
 will {\it not\/} be  active characters, but will
 have category code~ *11* (so that normally they won't
even appear in the input file).
 For~*@* this is easy to arrange (indeed
it would be quite difficult to avoid), since all our definitions are going to
be made while *@* has category code~*11*; for~*~* we will simply declare
*\catcode`\~=11* at the beginning of our definitions, and return to
*\catcode`\~=\active* at the end.\pagelabel{sl}
Because these *~*'s 
 are not active, we do not
have to worry about their being expanded in any *\xdef*'s or *\write*'s,
 which will turn
out to be quite a convenience.



When we begin our document, with the *\document* command, if the
*.lax* file already 
exists (from a previous run),
it will be read in, line by line, and each line
\newbox\boxx \newbox\boxxi
\setbox0\hbox{\<label\>}\setbox1\hbox{V$_{\text1}$}\setbox2
\hbox{V$_{\text2}$}\setbox3\hbox{V$_{\text3}$}\setbox4\hbox{V$_{\text4}$}%
\setbox5\hbox{\<type indicator\>}
**
@"copy0~"copy1~"copy2~"copy3~"copy4~"copy5
**
 will be
used to define `*\*\<label\>*@L*' to have the value
**
"copy1~"copy2~"copy3~"copy4~"copy5
**
  Thus, whenever a *.lax* file
already exists, we will start with all the information
obtained on the previous run.  Of course, we will have to make sure
that 
 *~* has category code~*11* while reading in the lines of the
*.lax* file so that it will have that category code when it is used 
in defining the corresponding control sequence
 (compare the remark on page~\ref{wcodes}).\pagelabel{wc2}



\section{\CS{ref} and its relatives}
 It should be pretty obvious how *\ref#1*,
*\Ref#1*, and other cross-referencing commands will work:
The test
**
\expandafter\ifx\csname#1@L\endcsname\relax
**
is true precisely when *#1* has not yet been used as a \<label\>.  If the
test is true, we simply give an error or warning message. Otherwise,
the value of *\csname#1@L\endcsname* will be 
\setbox1\hbox{V$_{\text1}$}\setbox2
\hbox{V$_{\text2}$}\setbox3\hbox{V$_{\text3}$}\setbox4\hbox{V$_{\text4}$}%
\setbox5=\hbox{\<type indicator\>}%
**
"box1~"box2~"box3~"box4~"box5
**
*\ref* will return
V$_{\text1}$, *\Ref* will return V$_{\text2}$, etc.

 The
really interesting question is how we are going to
keep the *\label* and *\pagelabel* information
updated. 

\section{{\tt\bs label}\label{label}}
Whenever we encounter a *\label{*\<label\>*}*,  we will first 
check that we are in a construction that allows \<label\>'s, using the test
(page~\ref{IFTL})
**
\ifx\thelabel@\relax "8IFTL2"8
**
If the result if true, so that we are in a construction not
allowing a \<label\>, 
 we will simply give an error message.  Otherwise, we will
use the test
**
\expandafter\ifx\csname#1@L\endcsname\relax
**
which is true if and only if *#1* has not already been used as a \<label\>.



If *#1* has not already been used as  \<label\>,  we will use
\setbox1\hbox{V$_{\text1}$}\setbox2
\hbox{V$_{\text2}$}\setbox3\hbox{V$_{\text3}$}\setbox4\hbox{V$_{\text4}$}%
\setbox5\hbox{\<type indicator\>}%
**
\expandafter\xdef\csname#1@L\endcsname{"copy1~"copy2~"copy3~"copy4~0}"8GGGG"8
**
the *0* at the end indicating that \<label\> comes from a *\label* added on
the current run.  In addition, we will
**
\immediate\write\laxwrite@{@#1~"copy1~"copy2~"copy3~"copy4~1}
**
with a *1* at the end.
When this line of the *.lax* file is read by *\document* on the next
run, `*\*\<label\>*@L*' will then be defined so that its value has
 a~*1* at the end, indicating that it
represents ``previous'' information.

On the other hand, if \<label\> {\it has\/} already been used,
we need to examine the whole sequence
\setbox0\hbox{\<label\>}\setbox1\hbox{V$_{\text1}$}\setbox2
\hbox{V$_{\text2}$}\setbox3\hbox{V$_{\text3}$}\setbox4\hbox{V$_{\text4}$}%
\setbox5\hbox{\<type indicator\>}
**
@"box0~...~...~...~...~"box5
**
and determine the value of the \<type indicator\>.

  If this value is *0* or
*2*,
then \<label\> has already been used on the current run, and we will just
give an
error message saying that \<label\> has already been used.\pagelabel{1or2}  

But if the value is *1* or *3*, then the information for \<label\> was
compiled during the previous run. Since we want to allow the previous value
to be changed, we will change the definition of `*\*\<label\>*@L*' so that
 the sequence 
\setbox0\hbox{\<label\>}
\setbox5\hbox{\<*1* or *3*\>}
**
...~...~...~...~"box5
**
that currently appears in the definition is replaced by the appropriate
\setbox0\hbox{\<label\>}\setbox1\hbox{V$_{\text1}$}\setbox2
\hbox{V$_{\text2}$}\setbox3\hbox{V$_{\text3}$}\setbox4\hbox{V$_{\text4}$}%
\setbox5\hbox{\<type indicator\>}
**
"box1~"box2~"box3~"box4~0
**
 the *0* once again indicating
that \<label\> now comes from a *\label* created
on the current run.\pagelabel{1or3}
And, once again, we will write appropriate
 information to the *.lax* file, but with
*1* replacing *0*.

\section{\CS{pagelabel}} The *\pagelabel* construction works rather
differently. First of all, we don't use the 
**
\ifx\thelabel@\relax
**
test, because *\pagelabel*'s are allowed anywhere.

So we simply start 
with the test
**
\expandafter\ifx\csname#1@L\endcsname\relax
**

  If this test is false, then
 then \<label\> has never been used, and
now we define `*\*\<label\>*@L*' to be\pagelabel{HH}
\setbox0\hbox{\<label\>}\setbox1\hbox{V$_{\text1}$}\setbox2
\hbox{V$_{\text2}$}\setbox3\hbox{V$_{\text3}$}\setbox4\hbox{V$_{\text4}$}%
\setbox5\hbox{\<type indicator\>}
**
"box1~"box2~"box3~"box4~2
**
 where 
the *2* at the end indicates that
\<label\> comes from a *\pagelabel* added on the current run, and where
\setbox4\hbox{value of *\page@N{\number\page@C}*}%
\setbox5\hbox{value of *\page@S{\page@P\page@N{\number\page@C}\page@Q}*}%
\setbox6\hbox{value of *\number\page@C*}%
\setbox7\hbox{value of *\page@P\page@N{\number\page@C}\page@Q*}%
$$
\align
 \hbox{V}_{\text1}&=\copy4\\
 \hbox{V}_{\text2}&=\copy5\\
 \hbox{V}_{\text3}&=\copy6\\
 \hbox{V}_{\text4}&=\copy7\endalign$$


As in the case of *\label*, we also want to write appropriate
 information to the
*.lax* file, except that the *2* at the end should be replaced  by
*3*, so that 
 when this line is read by *\document* in the next run, `*\*\<label\>*@L*'
will be defined with a~ *3* at the end, so that it
 will appear
as ``previous'' information.

  {\it But now there is a big difference:\/}
for *\label* we will use
 an *\immediate\write*, but for *\pagelabel* we will use
an ordinary *\write*.
  That is because only a (delayed) *\write* is certain
to give the proper value of *\page@C*---the information that we 
have recorded in *\*\<label\>*@L* may actually 
be incorrect, because the value of *\page@C*
 may not be the  number of the page
on which the *\pagelabel* eventually appears.
  And this means, of course, that only
*\pagelabel*'s read in from the {\it previous\/} run can be assured of
being correct.

\medbreak
The other case, when \<label\>
has already been used, also requires changes. As before, we
must examine the value
\setbox0\hbox{\<label\>}
\setbox5\hbox{\<type indicator\>}
**
...~...~...~...~"box5
**
of *\*\<label\>*@L*
and determine the value of the \<type indicator\>.

  If this value is *0* or
*2*,
then \<label\> has already been used on the current run, and we will just
give an
error message saying that \<label\> has already been used.  

On the other hand,
if the value is *1* or *3*, then the information for \<label\> was
compiled during the previous run. 

Now a
 *1* indicates that in the previous run
\<label\> was used for a *\label*, rather than a *\pagelabel*---presumably
because the user has now
decided to use \<label\>  for a *\pagelabel*
that was  used for a *\label* on the previous run.
  In this
case, we will simply replace the definition of `*\*\<label\>*@L*' with the
appropriate information for this new \<label\>, replacing the *1* with a
*2*.\pagelabel{HH2}
 We will also write corresponding new
information to the *.lax* file, changing the final *1* to a *3*, 
however,
so that when it is read in again on the next run, it will be recognized as
information coming from a previous *\pagelabel*.


On the other hand, a *3* indicates that
in the previous run \<label\> was used for a *\pagelabel*.  In this case,
as indicated above, this previously obtained information is more likely to be
the correct one.  Consequently, we will {\it not\/} change the 
definition of `*\*\<label\>*@L*'.
  But we will still write this appropriate new information
(using a delayed *\write*) to the *.lax* file, keeping the final *3*,
so that it will appear once again as ``previous'' information
on the next run.

\small The label mechanism in version~*2* of \lamstex\ is entirely different,
and much more efficient than, the one used in version~*1* of \lamstex@,
 which was designed using a
\tex\ that allowed 3,000 control sequence names.  Since \lamstex\ itself uses
up about 2,700 names, not counting additional control sequences introduced by
style files, 
it seemed imprudent at that time
to use a labelling method that introduces a
new control sequence name for each \<label\>.  But with that old mechanism,
main memory was usually exhausted after only about~40
or~50 \<label\>'s had been created (necessitating the stratagems explained in
section~4.8 of the \lamstex~Manual), so this excessive wariness was clearly 
counterproductive.  Moreover, more generous \tex s, allowing at least
3,500 control sequence names, are now quite common (and there's always
*tinylams.tex* for the truly parsimonious).
\endsmall




\chapter Beginning the document\label{BD} \endchapter
\section{Preliminaries\label{BDP}}
Since we have to read an existing *.lax* file at the beginning of the
document, and then write to a new *.lax* file during the document, we first
declare 
\C**
\newread\laxread@    "8lax"8
\newwrite\laxwrite@
**

\lamstex\  makes use of  a special sort of list,
initially defined to be empty,
\C**
\let\fnpages@=\empty
**
which is used for fancy footnote numbering.
As we will see in Chapter~\ref{foot}, when *\fancyfootnotes* is in effect,
each *\footnote*  will cause
\lamstex\ to write a special line to  the *.lax*  file: If the first
 footnote occurs on  page~ 7, say, then 
**
F7
**
will  be written to the *.lax* file.  If the second and third
footnotes
occur on  pages~ 12 and~14, then the lines
**
F12
**
and 
**
F14
**
will each be written (sometime later on).
  These lines are always  written with  a (delayed) 
*\write*, and the corresponding
information is {\it not\/} recorded  internally.  On  the other
hand, when we read in an existing *.lax* file, any such  *F*\<number\>
lines will be incorporated into *\fnpages@*, which will end up looking like
**
\\7\\12\\14 . . .
**
(As we will see in section~\Sref{FFN}, we will be able to
 extract information from
*\fnpages@* in an extremely efficient way.)
For this purpose, we will be using
\C**
\def\Finit@#1#2\Finit@{\let\nextii@=#1\def\nextiii@{#2}}
**
so that *\Finit@...\Finit@* will *\let\nextii@* be the first
token in `*...*' 
and define *\nextiii@* to be the remainder. (Since *\Finit@* will  always
be  applied to a line we read in from the *.lax* file, *\nextii@* will
always be either *F* or *@*.)

At this point, *lamstex.tex* changes *~* to a letter, and introduces
the routine
*\getparts@*:
\C**
\catcode`\~=11
"slip
\def\getparts@ @#1~#2~#3~#4~#5~#6{\def\nextiv@{#1}%
 \def\nextiii@{#2~#3~#4~#5~}\count@=#6\relax}
**
Thus, when applied to something of the form
\setbox0\hbox{\<label\>}
\setbox1\hbox{V$_{\text1}$*~*V$_{\text2}$*~*V$_{\text3}$*~*V$_{\text4}$*~*}
\setbox2\hbox{\<type indicator\>}
**
@"box0~"copy1"box2
**
*\getparts@* stores \<label\> in *\nextiv@* and \box1\ in *\nextiii@*, and
sets *\count@* to the value of \<type indicator\>.


\section{\CS{document}}
As in \amstex@, *\document* first defines *\fontlist@* to be empty.
It then opens the file *\jobname.lax* for reading. It processes the
contents of this file one line at a time, reading each line into *\next@*.
This is done with a *\loop*, where we *\repeat* until *\ifeof* detects the
end of the file (see section~\Sref{LOOP}).


First we will see if *\next@* is a special line starting with
~*F* by  using the test
**
\expandafter\Finit@\next@\Finit@
\ifx\nextii@ F
**
If this test is true, then *\next@* is `*F*\<number\>', and
 *\nextiii@* has  been defined to be the \<number\>. We want to
add `*\\*\<number\>' to *\fnpages@*,
**
\expandafter\rightadd@\nextiii@\to\fnpages@
**

If the test is false, so that *\next@* is not one of the special lines
for fancy  footnote numbering,
then it will be of the form
\setbox0\hbox{\<label\>}
\setbox1\hbox{V$_{\text1}$*~*V$_{\text2}$*~*V$_{\text3}$*~*V$_{\text4}$*~*}
\setbox2\hbox{\<type indicator\>}
**
"copy0~"copy1"copy2
**
and we want to make the appropriate definition
\setbox5\hbox{`}\setbox6\hbox{'}
**
\def","box5\"copy0@L"box6",{"copy1"copy2}
**
To do this we use
**
\expandafter\getparts@\next@
**
and then
**
\edef\next@{\gdef\csname\nextiv@ @L\endcsname "8ADDCSNAME"8
 {\nextiii@\number\count@}
\next@
**
Here the *\edef* makes *\next@* mean
\setbox3\hbox{\<label\>}%
**
"9\gdef"9","9\"copy3"relax@L"9{"9"copy1"relax"9"copy2}
**
The control sequence `*\*\copy0*@L*' is not expanded further because it
 has been made equal to *\relax*. 
As noted on page~\ref{necc}, any control sequences appearing in *\next@* 
 should be ones whose expansion is inhibited by
*\noexpands@*; 
so \copy1\ will not be expanded further,
because we will be doing all this within a group with *\noexpands@*.
\pagelabel{A1}
 In addition, as we mentioned on
page~\ref{wc2}, we will want to make *@* and *~* have category
code~*11* within this group.
Finally, we will set
**
\endlinechar=-1
**
within this group, so that *\next@* will not contribute a blank space at
the end because of the \CR\ at the end of the line.

There is one further
detail  that we  have to worry about.
Many files, especially files that have been written by \tex\ itself, have a
\CR\ at the end.  In this case, the last *\next@* before the end of the
file will be empty (if we hadn't set *\endlinechar=-1* it would be
*\par*). Consequently, 
**
\expandafter\Finit@\next@\Finit@
**
and
**
\expandafter\getparts@\next@
**
would give error messages.
  So, before any of our tests, 
we will first make sure that *\next@* isn't empty.

After having read *\jobname.lax*, and thus obtaining all the information
form the last run of the file, we re-open the file, to record information
produced with this run:
\C**
\def\document{\let\fontlist@=\empty
 \immediate\openin\laxread@=\jobname.lax\relax
"2
 {\endlinechar=-1 \noexpands@
  \catcode`\@=11 \catcode`\~=11
"2
  \loop \ifeof\laxread@ \else
   \read\laxread@ to\next@
"2
   \ifx\next@\empty
"2
   \else
    \expandafter\Finit@\next@\Finit@
"2
    \ifx\nextii@ F%
     \expandafter\rightadd@\nextiii@\to\fnpages@
"2
    \else  
     \expandafter\getparts@\next@
     \edef\next@{\gdef\csname\nextiv@ @L\endcsname
      {\nextiii@\number\count@}}%
     \next@
    \fi
   \fi
  \repeat}%
 \immediate\closein\laxread@
 \immediate\openout\laxwrite@=\jobname.lax\relax}
**


\chapter Labels\label{LBL2}\endchapter
\section{\CS{label}}
We begin by setting
\C**
\let\thelabel@=\relax
**
(see pages~\ref{IFTL} and~\ref{IFTL2}).
Since the combination 
**
\thelabel@ ~\thelabel@@ ~\thelabel@@@ ~\thelabel@@@@ ~
**
occurs several times in our constructions, it will save time and space to
introduce an abbreviation for it:
\C**
\def\thelabels@{\thelabel@ ~\thelabel@@ ~\thelabel@@@ 
 ~\thelabel@@@@ ~}
**

The definition of *\label#1*  begins with *\prevanish@*, since
*\label*'s are supposed to be invisible,
and then
 gives an error message if *\thelabel@* is *\relax*, so that
 we are not in a construction that allows
*\label*'s.
Otherwise we first use the test
**
\expandafter\ifx\csname#1@L\endcsname\relax
**
which is true precisely when *#1* has
 not already been used as a \<label\>. In this case,
we simply use 
**
\expandafter\xdef\csname#1@L\endcsname{\thelabels@0}
\immediate\write\laxwrite@{@#1~\thelabels@1}
**
to define `*\#1@L*'  and
to write to the *.lax* file. Of course, this must
be done within a group with *\noexpands@*.\pagelabel{A2}

If *#1* has already been used as a \<label\>,
 then we need to look at the \<type
indicator\> of `*\#1@L*'.  To do this we use
**
\edef\next@{@~\csname#1@L\endcsname}
\expandafter\getparts@\next@
**
so that *\count@* will have the value of \<type indicator\>.
We need the *\edef\next@* so that *\next@* will contain
 the actual value that
the control sequence
*\csname#1@L\endcsname* expands out to; naturally, we also need to perform
this step in a group with *\noexpands@*.


If, as a result of our test, *\count@* is even, we  issue an error
message that label *#1* has already been used. Otherwise, we
simply use
**
\expandafter\xdef\csname#1@L\endcsname{\thelabels@0}  
\immediate\write\laxwrite@{@#1~\thelabels@1}
**
to define the control sequence and write to the *.lax* file:
\C**
\def\label#1{\prevanish@
 \ifx\thelabel@\relax
  \Err@{There's nothing here to be labelled}%
"2
 \else
  {\noexpands@
"2
  \expandafter\ifx\csname#1@L\endcsname\relax
   \expandafter\xdef\csname#1@L\endcsname{\thelabels@0}%
   \immediate\write\laxwrite@{@#1~\thelabels@1}%
"2
  \else 
   \edef\next@{@~\csname#1@L\endcsname}%
   \expandafter\getparts@\next@
"2
   \ifodd\count@
    \expandafter\xdef\csname#1@L\endcsname{\thelabels@0}%
    \immediate\write\laxwrite@{@#1~\thelabels@1}%
"2
   \else
    \Err@{Label #1 already used}%
   \fi
  \fi
  }%
 \fi
 \postvanish@}
**
For simplicity, we used a single group to enclose all the constructions that
require a *\noexpands@*.



Finally, having defined *\label* we now
\C**
\rightadd@\label\to\vanishlist@
**

\section{\CS{pagelabel}}
There are several differences between 
the definition of *\pagelabel* and that of 
*\label*. 

\Pitem First of all, we don't have to check the value of *\thelabel@*,
since *\pagelabel* is allowed anywhere.

\pitem\label{EN}
 Instead of *\thelabel@*,
\dots, *\thelabel@@@@*, which are defined by constructions that can be
given a \<label\>, 
we  
use the values we want for a page label. Again, it will save time and space
to introduce an abbreviation:
\C**
\def\thepages@{\page@N{\number\page@C}~%
 \page@S{\page@P\page@N{\number\page@C}\page@Q}~%
 \number\page@C ~\page@P\page@N{\number\page@C}\page@Q ~}
**
(As with *\thelabels@*, we will be using *\thepages@* within a group where we
have stated *\noexpands@*.)

\pitem
Instead of an
*\immediate\write\laxwrite@*, we
must use a (delayed)
 *\write\laxwrite@*.
This is necessary to be sure of getting the proper value of
*\page@C* into the *.lax* file. 


\smallskip

When we encounter a *\pagelabel#1*, we again first use the test
**
\expandafter\ifx\csname#1@L\endcsname\relax
**
which is true if *#1* has not already been used as a \<label\>; in this
case, we  simply use
**
\expandafter\def\csname#1@L\endcsname{\thepages@2}
\write\laxwrite@{@#1~\thepages@3}
**

If the test is not true, we again need to look at the type indicator with
**
\edef\next@{@~\csname#1@L\endcsname}
\expandafter\getparts@\next@
**
If this test sets *\count@* to be even, we issue an error message.
But if *\count@* is odd we always
**
\write\laxwrite@{@#1~\thepages@@3}
**
moreover, we also
**
\expandafter\xdef\csname#1@L\endcsname{\thelabels@2}
**
if *\count@* is *1* (but not if it is *3*):
\C**
\def\pagelabel#1{\prevanish@
 \expandafter\ifx\csname#1@L\endcsname\relax
"2
  {\noexpands@
  \expandafter\xdef\csname#1@L\endcsname{\thepages@2}}%
  \write\laxwrite@{@#1~\thepages@3}% 
"2
 \else 
"2
  {\noexpands@
  \edef\next@{@~\csname#1@L\endcsname}%
  \expandafter\getparts@\next@
"2
  \ifodd\count@
   \ifnum\count@=1
    \expandafter\xdef\csname#1@L\endcsname{\thelabels@2}%
   \fi
   \write\laxwrite@{@#1~\thepages@3}%
"2
  \else
   \Err@{Label #1 already used}%
  \fi
  }%
 \fi
 \postvanish@}
**
For simplicity, we have again used a single group for all constructions
that require the *\noexpands@*. The *\write* happens to appear in this
group, but as before (page~\ref{SUB1}),
 that is irrelevant, since the *\write* only happens
during a *\shipout*.\pagelabel{SUB99}


Finally, we add *\pagelabel* to *\vanishlist@*:
\C**
\rightadd@\pagelabel\to\vanishlist@
**



Page~39 of the \lamstex~Manual mentions that  for a counter, say\linebreak
`*\somecounter*',
 we want to allow such things
as 
**
\pagelabel{thispage\number\somecounter} 
**
In version ~*1* of \lamstex@, special manipulations were required for this,
but now both *\label* and *\pagelabel* automatically allow this, 
\pagelabel{EVNR}
because
in both cases the argument *#1* 
is  expanded out in all parts of the definition.



\chapter Cross-Referencing\label{xref}\endchapter

\section{Preliminaries}
We need a flag *\ifreferr@* to tell whether we want error messages or
merely warning messages when a \<label\> *#1* for a *\ref*
 isn't found:
\C**
\newif\ifreferr@
\referr@true
\def\RefErrors{\global\referr@true}
\def\RefWarnings{\global\referr@false}
**
And we want to define a routine that prints either the desired
error message or the desired
warning message.
 For \tex~ version *2*, the best we can do is the following, where
*\W@* from \amstex\ stands for `*\immediate\write16 *':
**
\ifreferr@\Err@{No \noexpand\label found for #1}\else
\W@{Warning: No \noexpand\label found for #1.}\fi}
**
(As before, compare section~\Sref{SACN} for the use of *\noexpand*.)

But in \tex~version *3*, we can mimic an error message more closely
by 
 printing the line number after the warning,
using *\inputlineno*:
**
\W@{Warning: No \noexpand\label found for #1.}
\W@{l.\number\inputlineno\space ... #1}
**
(We have to settle for `*...*' since we can't actually capture the contents
of the input line.)

It looks even better to print something like
**
l.3 ... \ref{#1}
**
when a \<label\> for *\ref* isn't found, and
**
l.3 ... \Ref{#1}
**
when a \<label\> for  *\Ref* isn't found, etc. So we will actually 
be creating a control sequence with two arguments,
 the first corresponding to the *\ref* or
*\Ref*, and the second to the \<label\>, so that we will print
**
\W@{Warning: No \noexpand\label found for #2.}
\W@{l.\number\inputlineno\space ... \string#1{#2}}
**

Since we can't be sure when people will be switching to version~*3*, it
seems best to use different code for the two versions.  We can check for the
version of \tex\ with
\setbox0\hbox{(here *0* is `zero', not `oh')}
**
\setbox0=\hbox{\global\count@=`^^30}    "box0
**
In \tex~version *3*, *\count@* will then have the value *48*, but in
\tex~version~*2*, it will have the value *115* (and *\box0* will also
contain the character *0*). Instead of running this test each time we have
to print a warning, we
will simply let `*\versionthree@*' be undefined in version~*2* and
*\relax* in version~*3*:
\C**
\setbox0=\hbox{\global\count@=`^^30}
\ifnum\count@=48 \let\versionthree@=\relax\fi
**
Then we can use a message of the form
**
\ifreferr@\Err@{No \noexpand\label found for #2}\else
\W@{Warning: No \noexpand\label found for #2.}%
\ifx\versionthree@\relax
 \W@{l.\number\inputlineno\space ... \string#1{#2}}\fi
\fi
**

(The *\global\count@* assignment here doesn't really contradict the 	
policy of section~\Sref{LANDG} because this *\global* assignment
is made just once, at the top level, not within a macro.)


\small
The simpler looking test
**
\setbox0=\hbox{\global\count@=`^^00}
**
has all sorts of  insidious complications, because in version~*3* of
\tex@, *^^00* stands for the {\ninerm ASCII} *NUL*, which
is usually an {\it ignored\/} character in \tex\,! Since *^^30* is the
code for the number *0*, it is unlikely to be special.
\endsmall

\section{\CS{ref} and its relatives\label{refED}}
For *\ref#1* we simply have to use the test
**
\expandafter\ifx\csname#1@L\endcsname\relax
**
to check whether *#1* is a label, and then pick out the relevant portion
of the value of *\csname#1@L\endcsname*.

With this in mind, we might first define *\nolabel@* by
**
\def\nolabel@#1#2{\expandafter\ifx\csname#2@L\endcsname\relax
 \ifreferr@\Err@{No \noexpand\label found for #2}\else
  \W@{Warning: No \noexpand\label found for #2.}%
  \ifx\versionthree@\relax
   \W@{l.\number\inputlineno\space ... \string#1{#2}}\fi
 \fi
 \else}
**
so that *\nolabel@#1#2* would give an error or warning message if 
*#2*
hasn't been used as a label, and otherwise do whatever follows. However, it
will be a little more convenient to define
 *\nolabel@#1#2#3*, with  an extra argument,~ *#3*,
that is
often given the value *\relax*:
\C**
\def\nolabel@#1#2#3{%
 \expandafter\ifx\csname#2@L\endcsname\relax
  \ifreferr@\Err@{No \noexpand\label found for #2}\else
   \W@{Warning: No \noexpand\label found for #2.}%
   \ifx\versionthree@\relax
    \W@{l.\number\inputlineno\space ... \string#1{#2}}\fi
  \fi
 #3\else}
**

We also want a routine that sets a scratch token to the actual value of
the control sequence 
*\csname#1@L\endcsname*; because this will have to be defined within a group,
we use the scratch token *\Next@*, reserved for *\global* assignments 
(page~\ref{GNXT}):
\C**
\def\csL@#1{{\noexpands@\xdef\Next@{\csname#1@L\endcsname}}}
**


Now *\ref#1* should print an error or warning message if *#1* is
not a \<label\>,
**
\def\ref#1{\nolabel@\ref{#1}\relax
 . . .
**
Otherwise, it should print everything up  to the first *~* in the value of
the control sequence
*\csname#1@L\endcsname*.
If we define
**
\def\nextii@#1~#2\nextii@{#1}
**
and also use 
**
\csL@{#1}
**
to set *\Next@* to the value of *\csname#1@L\endcsname*, then we
just have to use
**
\expandafter\nextii@\Next@\nextii@
**

So the definition of *\ref* is
\C**
\def\ref#1{\nolabel@\ref{#1}\relax   "8DEFREF2"8
 \def\nextii@##1~##2\nextii@{##1}%
 \csL@{#1}\expandafter\nextii@\Next@\nextii@\fi}
**
Similarly for
\C**
\def\Ref#1{\nolabel@\Ref{#1}\relax
 \def\nextii@##1~##2~##3\nextii@{##2}%
 \csL@{#1}\expandafter\nextii@\Next@\nextii@\fi}
**
and
\C**
\def\nref#1{\nolabel@\nref{#1}\relax
 \def\nextii@##1~##2~##3~##4\nextii@{##3}%
 \csL@{#1}\expandafter\nextii@\Next@\nextii@\fi}
**
and
\C**
\def\pref#1{\nolabel@\pref{#1}\relax
 \def\nextii@##1~##2~##3~##4~##5\nextii@{##4}%
 \csL@{#1}\expandafter\nextii@\Next@\nextii@\fi}
**

For later purposes, we will 
\C**
\let\pref@=\pref
**
so that *\pref@* may be used to reinstate the usual meaning of *\pref* if it
has been redefined.


The definition of *\Evaluatenref* is somewhat different---we 
 use the generality built into *\nolabel@* to
\hbox{*\gdef\Nref{-10000 }*} when *#1* isn't a label:
\C**
\def\Evaluatenref#1{%
 \nolabel@\Evaluatenref{#1}{\gdef\Nref{-10000 }}%
 \def\nextii@##1~##2~##3~##4~\nextii@{\def\nextii@{##3}}%
 \csL@{#1}\expandafter\nextii@\Next@\nextii@
 \xdef\Nref{\nextii@}\fi}
**
*\Evaluatepref* is analogous:
\C**
\def\Evaluatepref#1{%
 \nolabel@\Evaluatepref{#1}{\global\let\Pref=\empty}%
 \def\nextii@##1~##2~##3~##4~##5\nextii@{\def\nextii@{##4}}%
 \csL@{#1}\expandafter\nextii@\Next@\nextii@
 \xdef\Pref{\nextii@}\fi}
**

Note that the \<label\> 
 is expanded out in both *\nolabel@* and
*\csL@*.  Consequently (compare page~\ref{EVNR}), 
 *\Evaluatenref* and *\Evaluatepref* can have arguments containing
*\number\somecounter* for a counter `*\somecounter*';
 in fact, even *\ref*, *\Ref*,
*\pref* and *\nref* can  contain such arguments.

\small Applications of *\Evaluatenref* and *\Evaluatepref* are
given on pages~ 38@--39 of the \lamstex~Manual. `*\Evaluateref*' and
`*\EvaluateRef*' haven't been provided, on the grounds that 
in similar situations one would be able to determine the value of *\ref*
from that of *\nref*, and the value of *\Ref* from that of *\pref*.
\endsmall


\chapter Reading auxiliary files\label{RAF}\endchapter

Although *\readlax* is similar to *\document*,
  there are a few significant
differences.

\section{\CS{readlax}\label{rl}}
*\readlax#1*
  first opens the file *#1.lax* for reading, giving a conspicuous
message if the file isn't found, i.e., if the test *\ifeof* is true
at the beginning.
 (Note that *\document* {\it doesn't\/}
give a message if *\jobname.lax* isn't found.)
Like *\document*, it then processes the contents of this file
one line at a time, except that it will read the line into the control
sequence *\nextv@*.
Again, 
this is done with a *\loop* that repeats
until *\ifeof* detects the end of 
the file.


As with *\document*,
we want to ignore the case where *\nextv@* is empty. Now, however,
 we also want to ignore the lines
beginning with *F*, because
 information about the numbering of footnotes
from another file would
conflict with information gathered for the current file.

 So the definition of *\readlax#1* begins
**
\def\readlax#1{\immediate\openin\laxread@=#1.lax\relax
 \ifeof\laxread@\W@{}\W@{File #1.lax not found.}\W@{}\fi
"2
 {\endlinechar=-1 \noexpands@
  \catcode`\@=11 \catcode`\~=11
  \loop \ifeof\laxread@ \else
   \read\laxread@ to\nextv@
   \ifx\nextv@\empty
"2
   \else
    \expandafter\Finit@\nextv@\Finit@
    \ifx\nextii@ F%
    \else
**

When a suitable line *\nextv@* has been found,
we use
**
\expandafter\getparts@\nextv@
**
to stores the \<label\> part of *\nextv@* in *\nextiii@*, the
value of the \<type indicator\> in the
counter *\count@*,
and 
the rest of *\nextv@*, except for the initial *~*, 
in *\nextiii@*.\pagelabel{OMITSQ}

Then we have to use the test
**
\expandafter\ifx\csname\nextiv@ @L\endcsname\relax
**
to see if the \<label\> part of *\nextv@* has already been used, because
this represents a conflicting use of \<label\>, so that we need to issue an
error message (remember that *\readlax* can be used at any time, possibly
after some \<label\>'s have already been made).

If this test is true, so that the \<label\> does not appear, 
we will define `*\*\<label\>*@L*' to be the remainder of *\nextv@*,
{\it except that we will change the\/} \<type indicator\> to~*0* if it is~*1*
and to~*2* if it is~*3*.  For this we can use
**
\edef\next@{\gdef\csname\nextiv@ @L\endcsname
 {\nextiii@\ifnum\count@=1 0\else 2\fi}}
\next@
**
(within a group with *\noexpands@*).

As a consequence of this arrangement,
 any \<label\> from the
auxiliary file that we read in with *\readlax* will count as a ``current''
label, so that if *\label{*\<label\>*}*  occurs later
in the file we will get
an error message, rather than changing the data for this \<label\>. That
seems like the reasonable arrangement, since we use *\readlax* to get
information from what is presumably a different part of the same document, 
and the same *\label{*\<label\>*}* shouldn't appear in two
different  parts of the document (at least, not if we intend to combine the
labels in the two parts with *\readlax*).

Our whole definition is
\C**
\def\readlax#1{\immediate\openin\laxread@=#1.lax\relax
 \ifeof\laxread@\W@{}\W@{File #1.lax not found.}\W@{}\fi
"2
 {\endlinechar=-1 \noexpands@
  \catcode`\@=11 \catcode`\~=11
"2
  \loop \ifeof\laxread@ \else
"2
   \read\laxread@ to\nextv@
   \ifx\nextv@\empty
"2
   \else
    \expandafter\Finit@\nextv@\Finit@
    \ifx\nextii@ F%
"2
    \else
     \expandafter\getparts@\nextv@
     \expandafter\ifx\csname\nextiv@ @L\endcsname\relax     
"2
      \edef\next@{\gdef\csname\nextiv@ @L\endcsname
       {\nextiii@\ifnum\count@=1 0\else 2\fi}}% 
      \next@
"2
     \else
      \Err@{Label \nextiv@\space in #1.lax already used}%
     \fi
    \fi
   \fi
  \repeat}%
 \immediate\closein\laxread@}
**

At this point we are finished with all definitions that involve *~* with
category code~*11*:
\C**
\catcode`\~=\active
**


\section{Style files\label{STYF}}
Control sequences to read in style files are simple:
\C**
\def\docstyle#1{\input #1.st\relax}
\def\predocstyle#1{\input #1.stf\relax}
\def\postdocstyle#1{\input #1.stb\relax}
**
