def myFct<N, N2>(u64[N] ignored) -> u64[N2] {
    assert(2*N == N2);
    return [0; N2];
}

const u32 N = 3;
const u32 N2 = 2 * N;

def main(u64[N] arg) -> bool {
    u64[N2] someVariable = myFct(arg);
    return true;
}