theorem Th116:
  for q,z,x holds (((q | ((x | x) | z)) | (q | ((x | x) | z))) |
  ((x | q) | ((z | z) | q))) = ((z | (x | q)) | ((q | q) | (x | q)))
proof
  let q,z,x;
  (z | z) | (z | z) = z by SHEFFER1:def 13;
  hence thesis by Th115;
end;
