//# run
main() {
    let v: u64;
    let ref_v: &mut u64;
label b0:
    v = 5;
    ref_v = &mut v;
    assert(*copy(ref_v) == 5, 42);
    *copy(ref_v) = 42; // safe to modify ref
    assert(*move(ref_v) == 42, 42);
    assert(copy(v) == 42, 42);
    return;
}