theorem Th111:
  for q,w,p holds (q | q) | ((w | w) | q) = (q | (((p | (p | p))
  | (p | (p | p))) | w)) | (q | (((p | (p | p)) | (p | (p | p))) | w))
proof
  let q,w,p;
  (((p | (p | p)) | (p | (p | p))) | (p | (p | p))) | q = q | q by Th101;
  hence thesis by Th73;
end;
