reserve V, C for set;
reserve A, B, D for Element of Fin PFuncs (V, C);
reserve s for Element of PFuncs (V,C);

theorem Th18:
  A c= B implies D ^ A c= D ^ B
proof
  D ^ A = A ^ D & D ^ B = B ^ D by Th3;
  hence thesis by Th14;
end;
