homotopy hypothesis-theorem
delooping hypothesis-theorem
stabilization hypothesis-theorem
n-category = (n,n)-category
n-groupoid = (n,0)-category
3-morphism
A 3-morphism in an n-category is a morphism between 2-morphisms.
For an abelian group, the 3-fold delooping is a 3-groupoid whose 3-morphisms are given by .