let L be non empty satisfying_Sheffer_1 satisfying_Sheffer_2 satisfying_Sheffer_3 ShefferStr ; :: thesis: for w, y, p being Element of L holds (w | (p | (y | (y | y)))) | (w | p) = w
let w, y, p be Element of L; :: thesis: (w | (p | (y | (y | y)))) | (w | p) = w
p | p = p | (y | (y | y)) by SHEFFER1:def 14;
hence (w | (p | (y | (y | y)))) | (w | p) = w by Th109; :: thesis: verum