Hi All, 1. The problem statement, all variables and given/known data This is algebraic proof of Vandermonde's identity: I am having some problem understanding how we reached the second last step and more importantly, last steps from revious steps. src::proofwiki.org I would be grateful if someone would elaborate it clearly. 2. Relevant equations Basically none that are relevant to answer my question. 3. The attempt at a solution I have no idea how we reached the last two steps. Thank You.