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 Th148:
  for z,w,x holds (w | (z | ((x | x) | w))) = w | (x | z)
proof
  now
    let x,w,p,z;
    ((((x | x) | w) | ((z | (p | (p | p))) | w)) | w) = w | (z | ((x | x)
    | w)) by Th143;
    hence w | (z | ((x | x) | w)) = w | (x | z) by Th147;
  end;
  hence thesis;
end;
