theorem
  len p = len the_arity_of c implies variables_in (c-trm p) =
  union {variables_in t where t is quasi-term of C: t in rng p}
proof
  assume len p = len the_arity_of c;
  then c-trm p = [c, the carrier of C]-tree p by Def35;
  hence thesis by Th88;
end;
