\\(\def\cat#1{{\mathcal{#1}}}\\)
Check that monoidal categories generalize monoidal preorders: a monoidal preorder is a
monoidal category \\((\cat{P},I,\otimes)\\) where, for every \\(p,q\in\cat{P}\\), the
set \\(\cat{P}(p,q)\\) has at most one element.