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 Th153:
  for w,q,p holds (p | q) | w = w | (q | p)
proof
  let w,q,p;
  w | (p | q) = (p | q) | w by Th83;
  hence thesis by Th152;
end;
