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 Th124:
  for x,y,z holds ((x | (((z | (z | z)) | (z | (z | z))) | y)) |
  (x | (((z | (z | z)) | (z | (z | z))) | y))) = x
proof
  let x,y,z;
  (x | x) | ((y | y) | x) = x by Th121;
  hence thesis by Th111;
end;
