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

let p, y, w be Element of L; :: thesis: (w | ((y | y) | y)) | (p | (p | p)) = w

w | w = w | ((y | y) | y) by Th70;

hence (w | ((y | y) | y)) | (p | (p | p)) = w by Th71; :: thesis: verum

let p, y, w be Element of L; :: thesis: (w | ((y | y) | y)) | (p | (p | p)) = w

w | w = w | ((y | y) | y) by Th70;

hence (w | ((y | y) | y)) | (p | (p | p)) = w by Th71; :: thesis: verum