fun equals1(a: Double, b: Double) = a.equals(b)

fun equals2(a: Double?, b: Double?) = a!!.equals(b!!)

fun equals3(a: Double?, b: Double?) = a != null && b != null && a.equals(b)

fun equals4(a: Double?, b: Double?) = if (a is Double && b is Double) a.equals(b) else null!!


fun box(): String {
    if ((-0.0).equals(0.0)) return "fail 0"
    if (equals1(-0.0, 0.0)) return "fail 1"
    if (equals2(-0.0, 0.0)) return "fail 2"
    if (equals3(-0.0, 0.0)) return "fail 3"
    if (equals4(-0.0, 0.0)) return "fail 4"

    return "OK"
}