
theorem
  for a, b being Ordinal holds a (+) succ b = succ(a (+) b)
proof
  let a, b be Ordinal;
  thus a (+) succ b = a (+) (b (+) 1) by Th90
    .= (a (+) b) (+) 1 by Th81
    .= succ(a (+) b) by Th90;
end;
