theorem Th95:
  for w,p holds ((p | p) | (p | (w | (w | w)))) = (((w | w) | p) |
  (((w | w) | (w | w)) | p))
proof
  let w,p;
  p | (w | (w | w)) = p | p by SHEFFER1:def 14;
  hence thesis by SHEFFER1:def 15;
end;
