theorem
 for K be set st I <= J & J <= K
  holds I <= K
 proof let K be set such that
A1: CutLastLoc I c= J and
A2: CutLastLoc J c= K;
   CutLastLoc I c= CutLastLoc J by A1,Th18;
  hence CutLastLoc I c= K by A2;
 end;
