consider h being Homomorphism of L1,L2;
take h ; :: thesis: for a, b being Element of L1 holds h . (a "/\" b) = (h . a) "/\" (h . b)
thus for a, b being Element of L1 holds h . (a "/\" b) = (h . a) "/\" (h . b) by LATTICE4:def 1; :: thesis: verum