theorem
  for T being quasi-type of C for a being quasi-adjective of C holds
  vars (a ast T) = (vars a) \/ (vars T)
proof
  let T be quasi-type of C;
  let a be quasi-adjective of C;
  thus vars (a ast T) = varcl((variables_in a)\/variables_in T) by Th102
    .= (vars a) \/ vars T by Th11;
end;
