let L be 0_Lattice; :: thesis: Bottom L is_a_unity_wrt the L_join of L

now

let u be Element of L; :: thesis: the L_join of L . ((Bottom L),u) = u
thus the L_join of L . ((Bottom L),u) = (Bottom L) "\/" u
.= u by LATTICES:14 ; :: thesis: verum

end;

hence Bottom L is_a_unity_wrt the L_join of L by BINOP_1:4; :: thesis: verum