let N = 4;

// This uses the alternative nomenclature as well.

namespace Fibonacci(N);
    col fixed ISLAST(i) { if i == N - 1 { 1 } else { 0 } };
    col witness x, y;

    ISLAST * (y' - 1) = 0;
    ISLAST * (x' - 1) = 0;

    (1-ISLAST) * (x' - y) = 0;
    (1-ISLAST) * (y' - (x + y)) = 0;