theorem Th28:
 for k being Nat st k < LastLoc I & I <= J
  holds I.k = J.k
 proof let k be Nat such that
A1: k < LastLoc I;
 assume
A2: CutLastLoc I c= J;
A3: k in dom CutLastLoc I by A1,Th26;
  thus I.k = (CutLastLoc I).k by A1,Th27
       .= J.k by A2,A3,GRFUNC_1:2;
