What is the counter chain? Is this counter as in "program counter"? Or counter as in "against"? Something else?

@pmp I think that the counter chain referenced can be somewhat seen as the loop counter. There are no instructions so I think using the term program counter can be confusing. In this example, there doesn't seem to be an explicit counter because the loop from memory instead returns the result of the previous iteration. I generally think of counter chain as a "loop control" chain. In other examples you could forsure introduce an increment on the loopback in order to have a proper loop counter, but here the loop is defined another way.

I agree with @I-henken that in general, we would need a counter for count the number of iterations for the loop. Although in this case we don't have to.