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A counter-example finder for higher-order logic, designed to be used from various proof assistants. A spiritual successor to Nitpick. Documentation at

Nunchaku requires CVC4 1.5 or later. Alternatively, it can use other backends:

We have a set of problems for tests and regressions, that can also be helpful to grasp the input syntax and see how to use the constructs of Nunchaku.

Basic Usage

After installing nunchaku (see Build/Install) and at least one backend, call the tool on problem files written in one of the accepted syntaxes (Input/Output/Solvers) as follows:

$ git clone
$ nunchaku nunchaku-problems/tests/first_order.nun
SAT: {
  type term := {$term_0, $term_1}.
  type list := {$list_0, $list_1}.
  val nil := $list_1.
  val a := $term_1.
  val b := $term_0.
  val cons :=
    (fun (v_0/75:term) (v_1/76:list).
       if v_0/75 = $term_0 then $list_0 else if v_1/76 = $list_0 then $list_1
       else $list_0).}
{backend:smbc, time:0.0s}

A list of options can be obtained by calling nunchaku --help. A few particularly useful options are:

  • --help for listing options.

  • --timeout <n> (or -t <n>): maximal amount of seconds before returning "unknown"

  • j <n> for controlling the number of backend solvers active at the same time.

  • --solvers s1,s2 (or -s s1,s2) for using only the listed solvers.

  • --debug <n> (where n=1,2,…5) to enable debug printing. The maximal verbosity level is 5, and it is very verbose. Consider using nunchaku --debug 5 foo.nun | less -R to not drown in pages of text.

  • --pp-all (and each --pp-<pass>) for printing the problem after each transformation.

  • -nc to disable colored output if your terminal does not support it..


There is a dedicated mailing list at (register). The issue tracker can be used for reporting bugs.


To build Nunchaku, there are several ways.

Released versions

Releases can be found on .


The easiest way is to use opam, the package manager for OCaml. Once opam is installed (don’t forget to run eval `opam config env` when you want to use opam), the following should suffice:

opam pin add -k git nunchaku

then opam should propose to install nunchaku and its dependencies. To upgrade:

opam update
opam upgrade nunchaku

Note that the binary is called 'nunchaku.native' until is it installed.


You need to install the dependencies first, namely:

Once you have entered the source directory, type:



Free software under the BSD license. See file 'LICENSE' for more details.


Supported input formats are:

  • nunchaku’s own input format, ML-like (extension .nun)

  • TPTP (very partial support, extension .p)

  • TIP (extension .smt2)

Supported solver backends:

How to make a release

  • udpate the repository itself

    • edit nunchaku.opam to change version number

    • git commit --amend to update the commit

    • git tag 0.42

    • git push origin stable --tags

  • make an archive:

    • tar.gz: git archive --prefix=nunchaku/ 0.42 -o nunchaku-0.42.tar.gz

    • zip: git archive --prefix=nunchaku/ 0.42 -o

  • upload the archive on gforge, write some release notes, send a mail.