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 Th108:
  for x,y holds (y | (((y | (x | x)) | (y | (x | x))) | (x | y))) = x | y
proof
  let x,y;
  (x | y) | (y | (x | x)) = y by Th105;
  hence thesis by Th102;
end;
