Double Decks choose m cards from 2 decks of n cards (+1+x)(唱+2+x)…(a%+x%+x品) coefficient of m-order terms coefficient of xmm in (1+x+x2)"coefficient Double Decks (x0 1 + x1 1 + x2 1) (x0 2 + x1 2 + x2 2) ···(x0 n + x1 n + x2 n) of m-order terms (1 + x + x2) n coefficient of xm in 2 deck of s n cards choose m cards from