let L be non empty satisfying_Sheffer_1 satisfying_Sheffer_2 satisfying_Sheffer_3 ShefferStr ; :: thesis: for v, p, y, x being Element of L holds p | (x | v) = (v | ((x | (y | (y | y))) | p)) | p
let v, p, y, x be Element of L; :: thesis: p | (x | v) = (v | ((x | (y | (y | y))) | p)) | p
(p | p) | ((x | (y | (y | y))) | p) = p by Th121;
hence p | (x | v) = (v | ((x | (y | (y | y))) | p)) | p by Th142; :: thesis: verum