# Kronecker delta simplification involving fractions?

GROUPS:
 Hi guys, how are you all doing? I hope that you are all doing fine!So, I just started to make use of Mathematica few months ago, therefore I dont know if it's a silly question. I have the following the kind of term to be simplified Sum[{A[l, l1, i, j, k, l]/B[j, j + 1, i, j]} KroneckerDelta[i, l], {i, 0, \[Infinity]}] However, looks like that Mathematica is not able to solve it. It just returns the same expression. But, if I change the Kronecker delta argument to [i,10], instead of [i,l], the sum is simplified.I'd like to know if there's a way to simplify this kind of expression, since it does simplify this kind of sum, if there is no fraction. I mean: Sum[A[l, l1, i, j, k, l] KroneckerDelta[i, l], {i, 0, \[Infinity]}] 
 Carl Woll 2 Votes Wrap your sum in Assuming[Element[l, Integers], expr], for example: Assuming[ Element[l, Integers], Sum[{A[l, l1, i, j, k, l]/B[j, j + 1, i, j]} KroneckerDelta[i, l], {i, 0, \[Infinity]}] ] //InputForm (* {Piecewise[{{A[l, l1, l, j, k, l]/B[j, 1 + j, l, j], l >= 0}}, 0]} *)