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 | p) = w
let p, w be Element of L; :: thesis: (w | (p | p)) | (w | p) = w
p | w = w | p by Th83;
hence (w | (p | p)) | (w | p) = w by Th106; :: thesis: verum