> Kotlin's sequence pre-dates co-routines.

You misunderstood. The `Sequence` type does predate coroutines. But I meant the `sequence` builder function, which takes a block of suspending code to create a `Sequence`.

The in-order traversal in the article can be translated to Kotlin:

    fun walk(t: Tree?): Sequence<Int> = sequence {
        if (t != null) {
            yieldAll(walk(t.left))
            yield(t.value)
            yieldAll(walk(t.right))
        }
    }

As I have noted above, this is a use of coroutines that has nothing to do with concurrency.