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 Th76:
  for p,x holds x = (x | x) | ((p | p) | p)
proof
  let p,x;
  (x | x) | (x | x) = x by SHEFFER1:def 13;
  hence thesis by Th70;
end;
