package hol2dk

  1. Overview
  2. Docs
HOL-Light to Dedukti/Lambdapi translator


Dune Dependency






HOL-Light to Dedukti/Lambdapi translator

Published: 22 Nov 2023


Export HOL-Light proofs to Dedukti, Lambdapi and Coq

This project provides several things:

  • scripts patch and unpatch to (un)patch HOL-Light to dump proofs

  • a program hol2dk with commands for dumping proofs from HOL-Light, translate those proofs to Dedukti and Lambdapi, and generate Makefile's to translation those proofs to Coq using lambdapi.

HOL-Light is proof assistant based on higher-order logic, aka simple type theory.

Dedukti is a proof format based on the λΠ-calculus modulo rewriting (λ-calculus + simple types + dependent types + implicit type equivalence modulo user-defined rewriting rules).

Lambdapi is a proof assistant based on the λΠ-calculus modulo rewriting that can read and generate Dedukti proofs.

Coq is a proof assistant based on the Calculus of Inductive Constructions.

Installing HOL-Light sources


  • hol-light >= af186e9f3c685f5acab16097b05717c10ebb030d (28/01/23)

  • libipc-system-simple-perl

  • libstring-shellquote

  • ocaml 4.14.1

  • camlp5 8.00.05

  • ocamlfind

  • num

Find other potential working ocaml-camlp5 pairs on .

If you don't already have the HOL-Light sources somewhere, you can install them by using the following commands:

cd $HOME
sudo apt-get install -y libipc-system-simple-perl libstring-shellquote
-perl opam
opam init
opam switch create ocaml.4.14.1
eval `opam env`
opam install ocamlfind num camlp5
git clone --depth 1 -b master
make -C hol-light

Installing hol2dk


  • ocaml >= 4.13

  • dune >= 3.7

hol2dk is now available on Opam. To install it, simply do:

opam install hol2dk

For the moment, we however need hol2dk sources to run some commands (checking dk/lp files or translating them to coq).

You can also install hol2dk from its sources as follows:

git clone
cd hol2dk
dune build && dune install

Setting the environment variable $HOL2DK_DIR

For some commands to have access to files in hol2dk sources, you need to set the following environment variable:

export HOL2DK_DIR=   # absolute path to hol2dk source directory

In case you installed hol2dk using opam, write:

export HOL2DK_DIR=$OPAM_SWITCH_PREFIX/share/hol2dk

Patching HOL-Light sources


where $HOL_LIGHT_DIR is the directory where are the sources of HOL-Light.

This script slightly modifies a few HOL-Light files in order to dump proofs:

  • the HOL-Light kernel file defining types, terms, theorems, proofs and proof rules

  • HOL-Light file defining basic tactics corresponding to introduction and elimination rules of connectives

  • HOL-Light file defining basic tactics on equality

The patch also adds a file

Before applying the patch, a copy of these files is created in,, etc.

To restore HOL-Light files, simply do:

bash $HOL2DK_DIR/unpatch $HOL_LIGHT_DIR

You can add the option -y to force file restoration.

Summary of hol2dk commands

Get it by running hol2dk without arguments.

Dumping HOL-Light proofs

hol2dk dump

generates the files file.sig, file.prf and file.thm. should at least require until the line loads "";;.

WARNING: it is important to run hol2dk dump in the HOL-Light directory so as to compute the list of named theorems properly.

Generating dk/lp files from dumped files

The base theory in which HOL-Light proofs are translated is described in the files theory_hol.lp and

You first need to generate file.pos and file.use with:

hol2dk pos file
hol2dk use file

You can then generate with:


And file.lp with:

hol2dk file.lp

It is possible to get the proof of a single theorem by giving its number as additional argument (useful for debugging):

hol2dk file.lp $theorem_number

Generating dk/lp files in parallel

Dk/lp file generation is linear in the size of dumped files. For big dumped files, we provide a command to do file generation in parallel using make.

First generate file.dg and with:

hol2dk dg $nb_parts file
hol2dk mk file

where $nb_parts is the number of files in which you want to split the proofs.

Add links to hol2dk files:

ln -s $HOL2DK_DIR/
ln -s $HOL2DK_DIR/theory_hol.lp
ln -s $HOL2DK_DIR/lambdapi.pkg
ln -s $HOL2DK_DIR/coq.v
ln -s $HOL2DK_DIR/_CoqProject

Then generate with:

make -j $jobs -f dk

And file.lp with:

make -j $jobs -f lp

Checking the generated dk file

Requirement: lambdapi >= 2.3.0, dedukti >= 2.7 or kocheck

To check the generated dk file with dkcheck, do:

dk check

To check the generated dk file with the current version of kocheck, you need to slightly change the generated file:

sed -e 's/^injective /def /g' >
kocheck -j 7

Checking the generated lp files

Requirement: lambdapi >= 2.3.0 for single-threaded generated files, lambdapi master branch for multi-threaded generated files

To check the generated lp files with lambdapi, do:

lambdapi check --map-dir hol-light:. file.lp

or create a file lambdapi.pkg:

package_name = hol-light
root_path = hol-light

and simply do:

lambdapi check file.lp

Remark: In case hol-light and dkcheck/lambdapi do not use the same ocaml versions, it is convenient to use different switches in each directory:

Xterm 1 (for HOL-Light):

cd hol-light
opam switch link 4.02.3
eval `opam env`

Xterm 2 (for checking dk/lp files):

opam switch link 4.14.1
eval `opam env`

Translating lp files to Coq files

Requirement: lambdapi master branch

Once HOL-Light files have been translated to Lambdapi files, it is possible to translate Lambdapi files into Coq files using the Coq export feature of Lambdapi.

If your Lambdapi files have been generated using, you can simply do:

make -j $jobs -f v # to generate Coq files
make -j $jobs -f vo # to check the generated Coq files

To indicate a specific lambdapi command, do:

make -j $jobs -f LAMBAPI=$lambdapi v # to generate Coq files

Otherwise, you need to translate Lambdapi files one by one by hand or using a script:

lambdapi export -o stt_coq --encoding $HOL2DK_DIR/encoding.lp --erasing $HOL2DK_DIR/erasing.lp --renaming $HOL2DK_DIR/renaming.lp --requiring coq.v file.lp | sed -e 's/hol-light\.//g' > file.v

You can then check the generated Coq files as follows:

echo coq.v theory_hol.v file*.v > _CoqProject
coq_makefile -f _CoqProject -o Makefile.coq
make -j $jobs -f Makefile.coq


Dumping of

  • checking time without proof dumping: 1m14s

  • checking time with proof dumping: 1m44s (+40%)

  • dumped files size: 3 Go

  • number of named theorems: 2834

  • number of proof steps: 8.5 M (8% unused)

rule %
refl 29
eqmp 19
comb 17
term_subst 12
trans 6
type_subst 3
beta 3
abs 2
spec 2

Results on a machine with 32 processors i9-13950HX and 64 Go RAM:

Multi-threaded translation to Lambdapi with dg 100:

  • hol2dk dg: 14s

  • lp files generation time: 41s

  • lp files size: 1.9 Go

  • type abbrevs: 1.3 Mo

  • term abbrevs: 665 Mo (35%)

  • verification by lambdapi: 4h10 on 28 processors Intel Core Haswell @ 2.3 GHz with 16 Mo cache

  • translation to Coq: 30s 1.8 Go

  • verification by Coq: 2h29

Multi-threaded translation to Dedukti with dg 100:

  • dk file generation time: 1m9s

  • dk file size: 2.8 Go

  • type abbrevs: 1.3 Mo

  • term abbrevs: 752 Mo (27%)

  • kocheck: 6m19s

  • dkcheck: 6m22s

Single-threaded translation to Lambdapi (data of 12 March 2023):

  • lp files generation time: 12m8s

  • lp files size: 2.5 Go

  • type abbreviations: 460 Ko

  • term abbreviations: 787 Mo (31%)

Single-threaded translation to Dedukti (data of 12 March 2023):

  • dk files generation time: 22m37s

  • dk files size: 3.6 Go

  • type abbreviations: 524 Ko

  • term abbreviations: 820 Mo (23%)

Results for up to (by commenting from loads "" to the end) with dg 7:

  • proof dumping time: 12s 77 Mo

  • number of proof steps: 302 K (10% unused)

  • dk file generation: 3s 69 Mo

  • checking time with dk check: 9s

  • lp file generation: 2s 47 Mo

  • checking time with lambdapi: 1m15s

  • translation to Coq: 1s 45 Mo

  • checking time for Coq 8.18.0: 3m12s

Exporting pure Q0 proofs

Hol2dk instruments basic HOL-Light tactics corresponding to introduction and elimination rules of connectives to get smaller proofs and proofs closer to natural deduction proofs. It is however possible to generate full Q0 proofs by doing after patching:

sed -i -e 's/.*Q0.*//' -e 's/START_ND*)//' -e 's/(*END_ND//'

Results on upto (by commenting from loads "" to the end):

  • ocaml proof dumping: 13.2s

  • number of proof steps: 564351

  • proof dumping: 1.4s 157 Mo

  • dk file generation: 45s 153 Mo

  • checking time with dk check: 26s

  • checking time with kocheck -j 7: 22s

  • lp file generation: 29s 107 Mo

  • checking time with lambdapi: 2m49s

Results on

  • ocaml cheking without proof dumping: 1m14s

  • ocaml proof dumping: 2m9s (+74%)

  • proof size file: 5.5 Go

  • number of proof steps: 14.3 M

rule %
refl 26
eqmp 21
term_subst 15
trans 11
comb 10
deduct 7
type_subst 4
abs 2
beta 2
assume 2

Source files

Modified HOL-Light files:

  • provides functions on lists, etc. required by A few lines are commented out so that it compiles with ocamlc.

  • defines types, terms, theorems, proofs and elementary proof rules.

  • defines basic tactics corresponding to introduction and elimination rules of connectives.

  • defines basic tactic(al)s on equality including alpha and beta-reduction. These files contain special comments that are removed to patch hol-light.

Additional files required for hol2dk:

  • main program of Hol2dk.

  • provides a few basic definitions.

  • functions on types, terms and other data structures.

  • functions for accessing proofs.

  • translation to Lambdapi of types, terms and proofs.

  • translation to Dedukti of types, terms and proofs.

  • functions to compute dependencies and theorems of HOL-Light files.

  • functions for dumping the index of named theorems.

  • slightly truncated version of the HOL-Light file used for testing.

Note that all these files can be used in the OCaml toplevel as well by removing the open instructions and by adding unset_jrh_lexer;; and set_jrh_lexer;; at the beginning and at the end of the file.

Files necessary for the export to Coq: encoding.lp, erasing.lp, renaming.lp, coq.v.


HOL-Light proof recording follows ProofTrace developed by Stanislas Polu in 2019.

Dependencies (2)

  1. dune >= "3.7"
  2. ocaml >= "4.13"

Dev Dependencies (1)

  1. odoc with-doc

Used by