Iterating over a set of elements in CPLEX OPL

Question

I am trying to model the following constrain in OPL. Here πG is string set.

$$ r >= \sum_{k=1}^{Np-1} y(k,k+1) \quad \quad \quad \quad ∀p∈ πG $$

Here is how I tried it in CPLEX OPL,

tuple Path {{string} nodes;}

{Path} paths = ...;

subject to{

 forall(p in paths)
        sum (node in p.nodes) Y[node][next(p.nodes,node)]  <= r;

 }

since i want to iterate till N-1 th element of set and apply function Y for k+1 th element i used "next" function. But here it iterates till N th element. Is it possible to do it using OPL notation to iterate till N-1 th element and get the k+1 th element in function?