§ Orthogonal morphisms

Two morphisms e: a -> b and m: x -> y are orthogonal iff for any (f, g) such that the square commutes:

a --e--> b
|        |
f        g
|        |
v        v
x --m--> y

then there exists a UNIQUE diagonal d: b -> x such that the the triangles commute: ( f = d . e) and ( m . d = g):

a --e--> b
|       / |
f      / g
|   /!d  |
v /      v
x --m--> y