gistfile1.kt

trait Inv<T> {
    var t: T
}

fun <T> some(t: Inv<T>): Inv<Inv<T>> {
    return object : Inv<Inv<T>> {
        override var t: Inv<T>
            get() = t
            set(value: Inv<T>) {
                t.t = value.t
            }
    }
}

trait A
trait B: A
trait C: B