let L be non empty satisfying_Sh_1 ShefferStr ; :: thesis: for x, y being Element of L holds x | ((y | x) | x) = y | x
let x, y be Element of L; :: thesis: x | ((y | x) | x) = y | x
((y | x) | (y | x)) | x = y | x by Th13;
hence x | ((y | x) | x) = y | x by Th10; :: thesis: verum