let L be non empty satisfying_DN_1 ComplLattStr ; :: thesis: for x, y, z being Element of L holds ((((((x + (y ` )) + z) ` ) + y) ` ) + (((y ` ) + y) ` )) ` = y
let x, y, z be Element of L; :: thesis: ((((((x + (y ` )) + z) ` ) + y) ` ) + (((y ` ) + y) ` )) ` = y
((x + (y ` )) + y) ` = ((y ` ) + y) ` by Th35;
hence ((((((x + (y ` )) + z) ` ) + y) ` ) + (((y ` ) + y) ` )) ` = y by Th9; :: thesis: verum