Portal:Category theory/Did you know

... that in higher category theory, there are two major notions of higher categories, the strict one and the weak one ?
... that factorization systems generalize the fact that every function is the composite of a surjection followed by an injection ?
... that in a multicategory, morphisms are allowed to have a multiple arity, and that multicategories with one object are operads ?
... that it is possible to define the end and the coend of certain functors ?
... that in the category of rings, the coproduct of two rings is their tensor product ?
... that the Yoneda lemma proves that any small category can be embedded in a presheaf category ?
... that it is possible to compose profunctors so that they form a bicategory?