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 Th93:
  for z,w,x holds ((((x | x) | w) | ((z | z) | w)) | ((w | (x | z)
) | (w | (x | z)))) = (((w | w) | (w | (x | z))) | (((x | z) | (x | z)) | (w |
  (x | z))))
proof
  let z,w,x;
  ((w | (x | z)) | (w | (x | z))) = (((x | x) | w) | ((z | z) | w)) by
SHEFFER1:def 15;
  hence thesis by SHEFFER1:def 15;
end;
