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From: eijkhout@s41.csrd.uiuc.edu (Victor Eijkhout)
Newsgroups: comp.text.tex
Subject: Re: TeX and marks
Keywords: mark
Message-ID: <1990Oct22.224527.28858@csrd.uiuc.edu>
Date: 22 Oct 90 22:45:27 GMT
References: <41700@eerie.acsu.Buffalo.EDU>
Sender: news@csrd.uiuc.edu (news)
Organization: UIUC Center for Supercomputing Research and Development
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mdeck@sybil.cs.Buffalo.EDU (Mary Deck) writes:

[ introduction deleted]

>	\if\topmark\botmark{Conventions}
>	\else\if\firsmark\botmark{Problem \firstmark}
>	     \else{Problems \firstmark--\botmark}
>	\fi\fi

>What I would like to know is:
>1)  WHY are those \if's not always true?
>2)  How can I compare marks?
About \if: this is a test for equality of *character codes*.
Therefore if there is something that is not a character,
it is expanded until after \if there are two things
that are either a charcter, or an unexpandable control 
sequences. All control sequences are the same for this test,
but they differ from all characters.

Now suppose \topmark is {ab}. Then \if\topmark\topmark
expands to \if ab\topmark. 'a' and 'b' are compared, are
unequal, and therefore...

The test you want is \ifx. I'm not quite sure what the 'x'
stands for, but I interpret it as `extensive equality'.
Quite likely it does exactly what you need.

>Loads of thanks in advance....

You're welcome.

>					....Mary

Victor.