angle N(h1 k1 l1) ^ N(h2 k2 l2) =

angle N(h1 k1 l1) ^ [U2 V2 W2] =

angle [U1 V1 W1] ^ N(h2 k2 l2) =

angle [U1 V1 W1] ^ [U2 V2 W2] =