Source PostScript (solidisoutface.pps)

%% syntaxe : solid i solidisoutface --> bool
%% true si i est l indice d une face externe, false sinon
/solidisoutface {
4 dict begin
   /i exch def
   solidgetinouttable /IO exch def
   /n1 IO 0 get def
   /n2 IO 1 get def
   n1 i le 
   i n2 le and
end
} def