let L be non empty satisfying_Sheffer_1 satisfying_Sheffer_2 satisfying_Sheffer_3 ShefferStr ; :: thesis: for p, x being Element of L holds x = (x | x) | ((p | p) | p)
let p, x be Element of L; :: thesis: x = (x | x) | ((p | p) | p)
(x | x) | (x | x) = x by SHEFFER1:def 13;
hence x = (x | x) | ((p | p) | p) by Th70; :: thesis: verum