Thus the notion of coroutine is *not composable*. By opposition, the
primitive notion of continulets is composable: if you build two
different interfaces on top of it, or have a program that uses twice the
-same interface in two parts, then assuming that both part independently
+same interface in two parts, then assuming that both part independently
work, the composition of the two parts still works.
A full proof of that claim would require careful definitions, but let us