% 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 26.15, p. III-379.
% Original source in file "macros6.TEX", starting line 1035.
\wlog{L: "prevmon.tip" ["macros6.TEX," l. 1035, p. III-379]}%
% This file DOES belong to format "texip."
\InputD{legdate.tip}
\catcode`\@ = 11
\def\PrevMonth #1#2#3#4{%
    \CheckDate{#1}{#2}{1}%
    #3 = #1\relax
    #4 = #2\relax
    \advance #4 by -1
    \ifnum #4 = 0
        #4 = 12
        \advance #3 by -1
    \fi
}
\catcode`\@ = 12