reserve L for satisfying_Sh_1 non empty ShefferStr;
reserve L for satisfying_Sheffer_1 satisfying_Sheffer_2 satisfying_Sheffer_3
  non empty ShefferStr;
reserve v,q,p,w,z,y,x for Element of L;

theorem Th158:
  for x,q,z,y holds ((x | y) | (x | (((y | (z | (z | z))) | (y |
  (z | (z | z)))) | q))) = ((x | y) | (x | (y | (z | (z | z)))))
proof
  let x,q,z,y;
  (((x | (y | (z | (z | z)))) | q) | x) = (x | (((y | (z | (z | z))) | (y
  | (z | (z | z)))) | q)) by Th154;
  hence thesis by Th157;
end;
