In CPS, continuations are often closures. But: those closures also close over the surrounding function's hidden continuation parameter k, and make essential use of it! The last continuation-lambda in the function has to call k to simulate the return.

Yes, but if you take 'stack' too literally here then you'll think that `call/cc` copies the stack, when maybe it really doesn't.

> Closures capture variables.

Variables, yes, including the return address of the frame in which those variables are if that return address is make explicit (e.g., because of CPS conversion).

And now you can see that closures can be continuations if they implicitly capture the stack.