public open class Z {
    val z: Int = 0
}

// SIBLING:
public class A(): Z() {
    var a: Int = 1

    public inner class B(): Z() {
        var b: Int = 1

        fun foo(): Int {
            return i(this@A, this@B)
        }
    }
}

fun i(a1: A, b1: A.B): Int {
    return a1.a + b1.b + a1.z + b1.z
}