/usr/share/doc/texlive-doc/generic/tex-ps/cmyk-hax/rules.tex is in texlive-generic-recommended 2016.20170123-5.
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1 2 3 4 5 6 | \def\RULES{\special{ps:
/v {/ruley exch def /rulex exch def V} def
/V {gsave newpath transform round exch round exch itransform
moveto rulex 0 rlineto 0 ruley neg rlineto rulex neg 0 rlineto
closepath fill grestore} def
}}
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