Source PostScript (uniqp.pps)

%% syntaxe : A B uniqp --> A B si A <> B, et A sinon
/uniqp {
4 dict begin
   count 4 ge {
      /yB exch def
      /xB exch def
      /yA exch def
      /xA exch def
      xA isnum {
         xB isnum {
            yA yB ne xA xB ne or {
               xA xB yA yB
            } {
               xA yA
            } ifelse
         } {
            xA xB yA yB
         } ifelse
      } {
         xA xB yA yB
      } ifelse
   } if
end
} def

%/uniqp {} def