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 Th70:
  for x,w holds w | ((x | x) | x) = w | w
proof
  let x,w;
  (x | x) | (x | x) = x by SHEFFER1:def 13;
  hence thesis by SHEFFER1:def 14;
end;
