let L be non empty satisfying_Sheffer_1 satisfying_Sheffer_2 satisfying_Sheffer_3 ShefferStr ; :: thesis: for w, p being Element of L holds (p | (w | w)) | (w | p) = p
let w, p be Element of L; :: thesis: (p | (w | w)) | (w | p) = p
(w | w) | p = p | (w | w) by Th83;
hence (p | (w | w)) | (w | p) = p by Th97; :: thesis: verum