let L be non empty satisfying_Sheffer_1 satisfying_Sheffer_2 satisfying_Sheffer_3 ShefferStr ; :: thesis: for p, w being Element of L holds (w | p) | (p | (w | w)) = p
let p, w be Element of L; :: thesis: (w | p) | (p | (w | w)) = p
(w | w) | p = p | (w | w) by Th83;
hence (w | p) | (p | (w | w)) = p by Th92; :: thesis: verum