reserve x,y for object,X for set,
  f for Function,
  R,S for Relation;

theorem Th5:
  for S being integer-valued Relation st R c= S holds R is integer-valued
proof
  let S be integer-valued Relation;
  assume R c= S;
  then
A1: rng R c= rng S by RELAT_1:11;
  rng S c= INT by Def3i;
  hence rng R c= INT by A1;
end;
