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 Th89:
  for q,w holds w | q = ((w | w) | (w | q)) | ((q | q) | (w | q))
proof
  now
    let y,q,w;
    (((w | q) | ((y | y) | y)) | ((w | q) | (w | q))) = (w | q) by Th78;
    hence w | q = ((w | w) | (w | q)) | ((q | q) | (w | q)) by Th88;
  end;
  hence thesis;
end;
