theorem Th6:
  ic in rng p & (ic = a:=b or ic = AddTo(a, b) or ic = SubFrom(a, b) or
  ic = MultBy(a, b) or ic = Divide(a, b))
  implies a in UsedILoc p & b in UsedILoc p
proof
  assume that
A1: ic in rng p and
A2: ic = a:=b or ic = AddTo(a, b) or ic = SubFrom(a, b) or ic = MultBy(
  a, b) or ic = Divide(a, b);
A3: UsedIntLoc ic = {a, b} by A2,SF_MASTR:14;
  UsedIntLoc ic c= UsedILoc p by A1,SF_MASTR:19;
  hence thesis by A3,ZFMISC_1:32;
end;
