# Sum...

#### yo79

Let m,n be two natural numbers. Prove that:
$$\displaystyle \displaystyle \sum\limits_{i=-m}^{n} (-1)^i \frac{(2m+i)! (2n-i)!}{((m+i)!)^2((n-i)!)^2}=1$$

Anyone?

#### limitkiller

yo79 could you please tell us where did you find this?