Summation over index domain

Hi, 

I am trying to model the following constraint:

with x as a nonnegative value indication the hours processed of job j-1 in time bucket t and Y as binary variable indicating that job j in time bucket t may start or not. The problem is that t is in the index domain and I need a summation over t’ based on t. 

How can I properly model this? I already have two indices for the set time buckets: t and h. But how do I model that x(i,j,t) is the same as x(i,j,h)? Preferably in one variable if that is possible? If I just simply say x(i,j,h) in the constraint I get the error: The parentheses in variable "x" do not match. Which is true since I modelled the variable as x(i,j,t).