TITLE: Untyped Higher Category Theory
QUESTION [6 upvotes]: I am currently trying to wade through the vast lake of higher category theory, a formidable task,or so it seems.
In the process, it has occurred to me that there is a basic analogy in place with various forms of type theories, typed logic, typed set theory, typed lambda calculus, etc.
In higher cats, one has 1-morphisms, 2-morphisms, and so on.
A fairly hierarchical structure, a ladder to infinity of sorts.
Now, whenever there are types, there is (almost) invariably an un-typed variant of the theory, which "forgets" the types. So I wonder if there is something along these lines already somewhere in the categorical endeavor.

I try to be a bit more precise:
imagine you are staring at a
N-category (let us stick to a strict
one, just for sake of simplicity),
from the top, and you forget all the
type labels. You see a fairly
complicated diagram of maps whose
endpoints are other maps, and so on
and so forth. Now try to axiomatize
such a structure. That would be an
untyped higher category (UHC).
Is there a reference for this structure? Now get rid of the strictness, and re-do the experiment. What kind of untyped higher categories are the result of stripping types from general higher cats?
In the example I mentioned, the UHC is
well-founded, in the sense that there
are some fellows (the ground objects) who
only point to themselves (I identify here the objects with their identity maps). Now,
eliminate this distinguished role of
objects and you will have a not well
founded UHC.
Is there a study of
not-well-founded categories, in a
similar spirit as there is a theory of
not well-founded sets?

REPLY [4 votes]: Hi Mirco, I'm putting my comment as an answer in case otherwise you don't find it. I wonder if you need the "n-arrows-only" approach.... where language of partial monoids replace categories. For example where objects and 1-arrows are treated on the same footing as 2-arrows in a double or 2-category in which the identities are provided by the source and target maps. Proposition: A small double category is precisely a set with two commuting partial monoid structures. (And a 2-category similarly but with an extra condition.) Would it be at all useful to you to try to do this for the n-fold or for the n case?