Homotopy Type Theory
Formalized Homotopy Theory

Here are some links to proofs about homotopy theory, formalized in homotopy type theory. Please add!

Maybe we could figure out a way not to duplicate stuff between this page and homotopy groups of spheres?

Ali: Results about homotopy groups of spheres should go there, everything else here.

Cast of characters so far: Jeremy Avigad, Guillaume Brunerie, Favonia, Eric Finster, Chris Kapulkin, Dan Licata, Peter Lumsdaine, Mike Shulman, Evan Cavallo

In progress



  • To do cohomology with finite coefficients, all we need is the boring work of defining /p\mathbb{Z}/p\mathbb{Z} as an explicit group.
  • Calculate some more cohomology groups.
  • Compute the loop space of this construction and use it to define spectra.

At least one proof has been formalized

Whitehead’s theorem


Eilenberg-MacLane space



Freudenthal Suspension Theorem

Freudenthal suspension theorem?

Implies π k(S n)=π k+1(S n+1)\pi_k(S^n) = \pi_{k+1}(S^{n+1}) whenever k2n2k \leq 2n - 2

  • Peter’s encode/decode-style proof, formalized by Dan, using a clever lemma about maps out of 2 n-connected types. This is the “95%” version, which shows that the relevant map is an equivalence on truncations.
  • The full “100%” version, formalized by Dan, which shows that the relevant map is 2n2n-connected.

Homotopy limits

  • Jeremy Avigad, Chris Kapulkin and Peter Lumsdaine arXiv Coq code

Van Kampen

van Kampen theorem

Covering spaces

Covering space?

  • Favonia’s proofs (link in flux due to library rewrite).


Blakers-Massey theorem?

  • Favonia/Peter/Guillaume/Dan’s formalization of Peter/Eric/Dan’s proof (link in flux due to library rewrite).
category: homotopy theory

Last revised on January 19, 2019 at 14:06:38. See the history of this page for a list of all contributions to it.