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 Th139:
  for q,w,y,x holds (((x | (y | (y | y))) | w) | ((q | q) | w)) |
  ((w | (x | q)) | (w | (x | q))) = w | (x | q)
proof
  let q,w,y,x;
  ((x | q) | (x | q)) | (w | (x | q)) = x | q by Th121;
  hence thesis by Th138;
end;
