>>173 追加

species って、nLabでは圏論なんだけど
望月 IUT4 §3では、ZFCの集合論みたく書いてある
はて はて？ （＾＾；

https://ncatlab.org/nlab/show/species
nLab
species
(抜粋)
1. Idea
A (combinatorial) species is a presheaf or higher categorical presheaf on the groupoid core(FinSet), the permutation groupoid.

A species is a symmetric sequence by another name. Meaning: they are categorically equivalent notions.

2. Definition
1-categorical

2-categorical

(∞,1) -categorical

Operations on species
There are in fact 5 important monoidal structures on the category of species.