Can the following expression be reduced to some more simplified expression?
$\sum_{j=0}^{k} \binom{n-a + m-j}{n-a} \times \binom{a-1 + j}{a-1}$
n,m and a are some positive constants with a < n and k < m.
Can the following expression be reduced to some more simplified expression?
$\sum_{j=0}^{k} \binom{n-a + m-j}{n-a} \times \binom{a-1 + j}{a-1}$
n,m and a are some positive constants with a < n and k < m.