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 Th79:
  for p,y,w holds ((w | ((y | y) | y)) | (p | (p | p))) = w
proof
  let p,y,w;
  w | w = (w | ((y | y) | y)) by Th70;
  hence thesis by Th71;
end;
