Regarding usage of unbounded array in nuXmv 2.0.0

Question

This is regarding the usage of int-array type variables provided in nuXmv.

Can anyone help us by providing a few example programs where a variable of type array integer of integer or something similar has been manipulated.

We have been trying to write simple programs that generate potentially infinite states wherein an input variable of unbounded array type is being used and we are getting the following error: left hand side of index sub-scripting is not an array.

The offending nuXmv program is given below.

MODULE main

IVAR 
    req : array integer of boolean;

    
VAR 
    counter : integer;
    index : integer;
ASSIGN
------------------------------------------------------  
    init(index) := 0;
    
    next(index) := index +1;
------------------------------------------------------
    init(counter) := 0;
        
    next(counter) := case
        req[index] : counter + 1;
        !req[index] : counter;
        TRUE : counter;     
    esac;