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
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
It is possible to use the HoTT library directly on the command line with the
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
without asking, you should probably customize set the variable
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
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
you have code ready to join the main library. When you make large
changes, feel free to include timing information in your commit
./etc/coq-scripts/timing/make-pretty-timed-diff.sh && git commit -at ./time-of-build-both.log, or see the comments at the
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
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!