let L be non empty satisfying_Sh_1 ShefferStr ; :: thesis: for x, y, z being Element of L holds x | ((y | ((x | z) | y)) | x) = y | ((x | z) | y)
let x, y, z be Element of L; :: thesis: x | ((y | ((x | z) | y)) | x) = y | ((x | z) | y)
(y | ((x | z) | y)) | (x | x) = x by Th52;
hence x | ((y | ((x | z) | y)) | x) = y | ((x | z) | y) by Th16; :: thesis: verum