Homotopy Type Theory is an interpretation of Martin-Löf’s intensional type theory into abstract homotopy theory. Propositional equality is interpreted as homotopy and type isomorphism as homotopy equivalence. Logical constructions in type theory then correspond to homotopy-invariant constructions on spaces, while theorems and even proofs in the logical system inherit a homotopical meaning. As the natural logic of homotopy, type theory is also related to higher category theory as it is used e.g. in the notion of a higher topos.
The HoTT library is a development of homotopy-theoretic ideas in the Coq proof assistant. It draws many ideas from Vladimir Voevodsky's Foundations library.
Installation details are explained in the file INSTALL.txt
. You will
need to compile a version of Coq which supports the -indices-matter
flag, universe polymorphism, and private types. At present, only Coq
trunk supports these features; it's available at
https://github.com/coq/coq/branches/trunk. The particular version of
Coq which the current version of this repository is compatible is
bundled as a git submodule.
If you are looking for an older version of HoTT which works with standard Coq, have a look
at the one tagged as pure-coq-8.3
. Note however that we do not support the old
library anymore.
It is possible to use the HoTT library directly on the command line with the hoqtop
script, but who does that?
It is probably better to use Proof General and
Emacs. When Proof General asks you where to find the
coqtop
executable, just point it to the hoqtop
script. If Emacs runs a coqtop
without asking, you should probably customize set the variable proof-prog-name-ask
to
nil
(in Emacs type C-h v proof-prog-name-ask RET
to see what this is about).
At the moment there is no hoqide
equivalent of coqide
, but getting one is high on our
to-do list.
Contributions to the HoTT library are very welcome! We use the “fork
and pull” model: to contribute, please create your own
fork and issue a pull
request when
you have code ready to join the main library. When you make large
changes, feel free to include timing information in your commit
message; run ./etc/coq-scripts/timing/make-pretty-timed-diff.sh && git commit -at ./time-of-build-both.log
, or see the comments at the
top of etc/coq-scripts/timing/make-pretty-timed-diff.sh
for more
detailed instructions and caveats. To make use of these scripts, you
must first run git submodule update --init --recursive
. Note that
if you create a new file, you must update Makefile_targets.mk
. We
suggest running make strict
rather than just make
, so that you
will get an error if you forget.
The library is released under the permissive BSD 2-clause license, see the file
LICENSE.txt
for further information. In brief, this means you can do whatever you like
with it, as long as you preserve the Copyright messages. And of course, no warranty!