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% This macro source file is from the four volume series
% "TeX in Practice" by Stephan von Bechtolsheim, published
% 1993 by Springer-Verlag, New York.
% Copyright 1993 Stephan von Bechtolsheim.
% No warranty or liability is assumed.
% This macro may be copied freely if no fees other than
% media cost or shipping charges are charged and as long
% as this copyright and the following source code itself
% is not changed. Please see the series for further information.
%
% Version: 1.0
% Date: May 1, 1993
%
%
% This source code is documented in 24.1.18.1, p. III-302.
% Original source in file "macros4.TEX", starting line 1096.
\wlog{L: "isprefix.tip" ["macros4.TEX," l. 1096, p. III-302]}%
% This file DOES belong to format "texip."
\InputD{compst.tip}
\InputD{strleng.tip}
\InputD{showx.tip}
\catcode`\@ = 11
\newif\if@PrefixResult
\newcount\@LengthPrefixString
\newcount\@LengthMainString
\def\PrefixConditional #1#2{% 
    TT\fi
    \StringLength{#1}%
    \@LengthMainString = \StringLengthResult
    \StringLength{#2}% 
    \@LengthPrefixString = \StringLengthResult
    \ifnum\@LengthMainString < \@LengthPrefixString
        \@PrefixResultfalse
    \else
        \@PrefixConditionalTwo{#1}{#2}% 
    \fi
    \if@PrefixResult
}
\def\@PrefixConditionalTwo #1#2{% 
    \edef\@PrefixBoth{#1#2}% 
    \edef\@PrefixTemp{% 
        \def\noexpand\@TestPrefix ####1#2####2\noexpand\@Del{% 
            \noexpand\if\noexpand\EmptyStringConditional{####1}%
        }% 
    }% 
    \ShowX\@PrefixTemp
    \@PrefixTemp
    \ShowX{\@TestPrefix}%
    \expandafter\@TestPrefix\@PrefixBoth\@Del
        \@PrefixResulttrue
    \else
        \@PrefixResultfalse
    \fi
}
\catcode`\@ = 12