Why is Mathematica assuming k==l and how do I make it not to?

*To*: mathgroup at smc.vnet.net*Subject*: [mg92588] Why is Mathematica assuming k==l and how do I make it not to?*From*: Aaron Fude <aaronfude at gmail.com>*Date*: Tue, 7 Oct 2008 07:04:51 -0400 (EDT)

As in Assuming[Element[{k, l}, Integers] , Integrate[Cos[k alpha] Cos[l alpha], {alpha, -Pi, Pi}]] I get 0 whereas the answer is Pi if k=l; Thanks! Aaron