predicate fzn_regular(array[int] of var int: x, int: Q, int: S,
                  array[int,int] of int: d, int: q0, set of int: F) =
    let {
        % If x has index set m..n-1, then a[m] holds the initial state
        % (q0), and a[i+1] holds the state we're in after  processing
        % x[i].  If a[n] is in F, then we succeed (ie. accept the string).
          int: m = min(index_set(x)),
          int: n = max(index_set(x)) + 1,
          array[m..n] of var 1..Q: a
    } in
        a[m] = q0 /\                    % Set a[0].
        forall(i in index_set(x)) (
            x[i] in 1..S /\             % Do this in case it's a var.
            a[i+1] = d[a[i], x[i]]      % Determine a[i+1].
        ) /\
        a[n] in F;                      % Check the final state is in F.