> But Puzzle 209 is about something more specific.

> So, let me give some hints.

> In Puzzle 209 the feasibility relation we're calling \$$\Phi\$$ is just any old feasibility relation from \$$\mathbb{N}\$$ to \$$\mathbb{N}\$$: it's a very famous one, with a name! Similarly for \$$\Psi\$$... and similarly for \$$\Phi \otimes \Psi\$$. So the answer to Puzzle 209 is a special case of a general result - a result I haven't stated yet. I'm trying to get people to guess this result based on this particular example.

They are the identity morphisms for their respective objects in the category of feasibility relations. Perhaps the general result you mean is that the tensor of identities gives the identity for the tensor of the objects.