let V be non empty right_complementable add-associative right_zeroed addLoopStr ; :: thesis: for v, w being Element of V st - v = - w holds
v = w
let v, w be Element of V; :: thesis: ( - v = - w implies v = w )
assume - v = - w ; :: thesis: v = w
hence v = - (- w)
.= w ;
:: thesis: verum