theorem
  for a being quasi-adjective of C holds a ast (a ast T) = a ast T
proof
  let a be quasi-adjective of C;
  thus a ast (a ast T)
  = [{a} \/ ({a} \/ adjs T), the_base_of (a ast T)]
    .= [{a} \/ {a} \/ adjs T, the_base_of (a ast T)] by XBOOLE_1:4
    .= a ast T;
end;
