theorem
  A |^ (1, 2) = A \/ (A ^^ A)
proof
  thus A |^ (1, 2) = A |^ 1 \/ A |^ (1 + 1) by Th28
    .= A \/ A |^ 2 by FLANG_1:25
    .= A \/ (A ^^ A) by FLANG_1:26;
end;
