Hi! I want to ask, is there anyway to create a list (or a set) inside of a set? I am dealing with

and I don’t know how to formulate the Kqjk. What I am thinking is, i is element of Kqjk and Kqjk is element of q, therefore index i is element of q. Does anyone have any suggestions?

Hi @Renger, this is the full code that I want to use:

zi and yq represent binary variables, in which if zi = 1, a service station is built at node i, 0 otherwise. and if yq = 1, flow on path q is feasible.
Basically I have all the data that is needed (the nodes, arcs, potential facility locations, and number of stations to be located). It is just I am really confused on how to integrate the q with Kqjk.