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

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

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

hence w | w = ((y | y) | y) | w by Th83; :: thesis: verum

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

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

hence w | w = ((y | y) | y) | w by Th83; :: thesis: verum