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 Th104:
  for y,w holds (w | w) | w = (y | y) | y
proof
  let y,w;
  (w | w) | ((y | y) | y) = w by Th76;
  hence thesis by Th103;
end;
