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 Th154:
  for w,p,q holds ((q | p) | w) | q = q | ((p | p) | w)
proof
  let w,p,q;
  w | (p | q) = (q | p) | w by Th153;
  hence thesis by Th146;
end;
