theorem Th115:
  for q,z,x holds (((q | ((x | x) | z)) | (q | ((x | x) | z))) |
((x | q) | ((z | z) | q))) = ((((z | z) | (z | z)) | (x | q)) | ((q | q) | (x |
  q)))
proof
  let q,z,x;
  ((x | q) | ((z | z) | q)) = ((q | ((x | x) | z)) | (q | ((x | x) | z)))
  by Th74;
  hence thesis by SHEFFER1:def 15;
end;
