Within one packet and group g, multiply its row affine factors and extract the coefficient prescribed by beta for modes TARGETED at g. Multiply this by product L_Z(X)^(beta_Z) for modes whose SOURCE is g. That product is the child packet entry modulo 2^p_t. Each mode has one target and one source, so each coefficient choice and each substitution occurs exactly once. With no target rows, a positive target exponent gives zero. With an empty source tile, L_Z=0: exponent zero contributes one and positive exponents contribute zero. All these rules also apply to isolated packet vertices.