Possible Incorrect Summation

*To*: mathgroup at smc.vnet.net*Subject*: [mg31034] Possible Incorrect Summation*From*: Richard Palmer <mapsinc at bellatlantic.net>*Date*: Fri, 5 Oct 2001 01:22:45 -0400 (EDT)*Sender*: owner-wri-mathgroup at wolfram.com

I believe Sum[ (-1)^k Binomial[2 n, k] Binomial[2k, k] Binomial[4n - 2k, 2n - k],{k,0,2n}] is a special case of Dixon's Identity and should equal Binomial[2n,n]^2. Previously the SymbolicSum package returned a value which could be simplified to the result. The latest version of Mathematica returns a value which is is not this result as can be seen by graphing the difference. What has changed?