The morphisms are geometric arrangements.

Let SQ denote some fixed 'outer square.' For concreteness, we may take this to be the unit square.

Then a morphism \\(f_k: \square_1,...,\square_k \rightarrow \square\\) is an arrangement of \\(k\\) subsquares within SQ.

Let SQ denote some fixed 'outer square.' For concreteness, we may take this to be the unit square.

Then a morphism \\(f_k: \square_1,...,\square_k \rightarrow \square\\) is an arrangement of \\(k\\) subsquares within SQ.