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 Th88:
  for y,q,w holds ((w | q) | ((y | y) | y)) | ((w | q) | (w | q))
  = ((w | w) | (w | q)) | ((q | q) | (w | q))
proof
  let y,q,w;
  (w | q) | (w | q) = (w | q) | ((y | y) | y) by Th70;
  hence thesis by SHEFFER1:def 15;
end;
