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 Th77:
  for y,w holds (w | w) | (w | ((y | y) | y)) = w
proof
  let y,w;
  w | w = w | ((y | y) | y) by Th70;
  hence thesis by SHEFFER1:def 13;
end;
