1. The equivalence of crossed complexes and ∞-groupoids;Brown;Cahiers Topologie Ge´om. Diffe´rentielle,1981
2. Group-like structures in general categories, I. Multiplications and comultiplications;Eckmann;Math. Ann.,1962
3. Closed categories;Eilenberg,1966
4. Lokal pra¨sentierbare Kategorien;Gabriel,1971
5. Adjoint functors;Kan;Trans. Amer. Math. Soc.,1958