theorem
  len p = len the_arity_of c implies
  vars (c-trm p) = union {vars 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 Th89;
end;
