let L be non empty satisfying_Sh_1 ShefferStr ; :: thesis: for x, y, z being Element of L holds x | (y | (z | (x | y))) = x | (y | y)
let x, y, z be Element of L; :: thesis: x | (y | (z | (x | y))) = x | (y | y)
set Y = z;
y | (x | (y | (z | (x | y)))) = y | y by Th34;
hence x | (y | (z | (x | y))) = x | (y | y) by Th27; :: thesis: verum