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 Th122:
  for x,y holds (y | x) | x = ((x | (y | y)) | (x | (y | y))) | ( y | x)
proof
  let x,y;
  (x | (y | y)) | (y | x) = x by Th106;
  hence thesis by Th119;
end;
