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

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

(x | x) | (x | x) = x by SHEFFER1:def 13;

hence w | ((x | x) | x) = w | w by SHEFFER1:def 14; :: thesis: verum

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

(x | x) | (x | x) = x by SHEFFER1:def 13;

hence w | ((x | x) | x) = w | w by SHEFFER1:def 14; :: thesis: verum