theorem Th2:
  for A, B being Sequence holds rng(A^B) = rng A \/ rng B
proof
  let A, B be Sequence;
  rng A c= rng(A^B) & rng B c= rng(A^B) by Th7A, Th8A;
  then A1: rng A \/ rng B c= rng(A^B) by XBOOLE_1:8;
  rng(A^B) c= rng A \/ rng B by Th2Lem;
  hence thesis by A1;
end;
