theorem Th4:
  GRZ-arity.'not' = 1 & GRZ-arity.'&' = 2 & GRZ-arity.'=' = 2
proof
  'not' in GRZ-ops by ENUMSET1:def 1;
  hence GRZ-arity.'not' = GRZ-op-arity.'not' by Lm10 .= 1 by Def3;
  '&' in GRZ-ops by ENUMSET1:def 1;
  hence GRZ-arity.'&' = GRZ-op-arity.'&' by Lm10 .= 2 by Def3;
  '=' in GRZ-ops by ENUMSET1:def 1;
  hence GRZ-arity.'=' = GRZ-op-arity.'=' by Lm10 .= 2 by Def3;
end;
