D-4.4 Ciphertext-to-Plaintext Addition

BGV’s ciphertext-to-plaintext addition scheme is almost the same as BFV’s scheme (Summary D-2.5 in §D-2.5). However, one difference is that it’s not the case that the plaintext polynomial $\mathrm{\Lambda }(X)$ to be added is scaled up by $\mathrm{\Delta }$, but it remains as $\mathrm{\Lambda }(X)$.