doc-src/Sledgehammer/sledgehammer.tex

mention MaSh in docs

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\title{\includegraphics[scale=0.5]{isabelle_sledgehammer} \\[4ex]
Hammering Away \\[\smallskipamount]
\Large A User's Guide to Sledgehammer for Isabelle/HOL}
\author{\hbox{} \\
Jasmin Christian Blanchette \\
{\normalsize Institut f\"ur Informatik, Technische Universit\"at M\"unchen} \\[4\smallskipamount]
{\normalsize with contributions from} \\[4\smallskipamount]
Lawrence C. Paulson \\
{\normalsize Computer Laboratory, University of Cambridge} \\
\hbox{}}

\maketitle

\tableofcontents

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\section{Introduction}
\label{introduction}

Sledgehammer is a tool that applies automatic theorem provers (ATPs)
and satisfiability-modulo-theories (SMT) solvers on the current goal.%
\footnote{The distinction between ATPs and SMT solvers is convenient but mostly
historical. The two communities are converging, with more and more ATPs
supporting typical SMT features such as arithmetic and sorts, and a few SMT
solvers parsing ATP syntaxes. There is also a strong technological connection
between instantiation-based ATPs (such as iProver and iProver-Eq) and SMT
solvers.}
%
The supported ATPs are E \cite{schulz-2002}, E-SInE \cite{sine}, E-ToFoF
\cite{tofof}, iProver \cite{korovin-2009}, iProver-Eq
\cite{korovin-sticksel-2010}, LEO-II \cite{leo2}, Satallax \cite{satallax},
SNARK \cite{snark}, SPASS \cite{weidenbach-et-al-2009}, Vampire
\cite{riazanov-voronkov-2002}, and Waldmeister \cite{waldmeister}. The ATPs are
run either locally or remotely via the System\-On\-TPTP web service
\cite{sutcliffe-2000}. In addition to the ATPs, the SMT solvers Z3 \cite{z3} is
used by default, and you can tell Sledgehammer to try Alt-Ergo \cite{alt-ergo},
CVC3 \cite{cvc3}, and Yices \cite{yices} as well; these are run either locally
or (for CVC3 and Z3) on a server at the TU M\"unchen.

The problem passed to the automatic provers consists of your current goal
together with a heuristic selection of hundreds of facts (theorems) from the
current theory context, filtered by relevance. Because jobs are run in the
background, you can continue to work on your proof by other means. Provers can
be run in parallel. Any reply (which may arrive half a minute later) will appear
in the Proof General response buffer.

The result of a successful proof search is some source text that usually (but
not always) reconstructs the proof within Isabelle. For ATPs, the reconstructed
proof relies on the general-purpose \textit{metis} proof method, which
integrates the Metis ATP in Isabelle/HOL with explicit inferences going through
the kernel. Thus its results are correct by construction.

In this manual, we will explicitly invoke the \textbf{sledgehammer} command.
Sledgehammer also provides an automatic mode that can be enabled via the ``Auto
Sledgehammer'' option in Proof General's ``Isabelle'' menu. In this mode,
Sledgehammer is run on every newly entered theorem. The time limit for Auto
Sledgehammer and other automatic tools can be set using the ``Auto Tools Time
Limit'' option.

\newbox\boxA
\setbox\boxA=\hbox{\texttt{NOSPAM}}

\newcommand\authoremail{\texttt{blan{\color{white}NOSPAM}\kern-\wd\boxA{}chette@\allowbreak
in.\allowbreak tum.\allowbreak de}}

To run Sledgehammer, you must make sure that the theory \textit{Sledgehammer} is
imported---this is rarely a problem in practice since it is part of
\textit{Main}. Examples of Sledgehammer use can be found in Isabelle's
\texttt{src/HOL/Metis\_Examples} directory.
Comments and bug reports concerning Sledgehammer or this manual should be
directed to the author at \authoremail.

\vskip2.5\smallskipamount

%\textbf{Acknowledgment.} The author would like to thank Mark Summerfield for
%suggesting several textual improvements.

\section{Installation}
\label{installation}

Sledgehammer is part of Isabelle, so you do not need to install it. However, it
relies on third-party automatic provers (ATPs and SMT solvers).

Among the ATPs, E, LEO-II, Satallax, SPASS, and Vampire can be run locally; in
addition, E, E-SInE, E-ToFoF, iProver, iProver-Eq, LEO-II, Satallax, SNARK,
Vampire, and Waldmeister are available remotely via System\-On\-TPTP
\cite{sutcliffe-2000}. If you want better performance, you should at least
install E and SPASS locally.

Among the SMT solvers, Alt-Ergo, CVC3, Yices, and Z3 can be run locally, and
CVC3 and Z3 can be run remotely on a TU M\"unchen server. If you want better
performance and get the ability to replay proofs that rely on the \emph{smt}
proof method without an Internet connection, you should at least install Z3
locally.

There are three main ways to install automatic provers on your machine:

\begin{sloppy}
\begin{enum}
\item[\labelitemi] If you installed an official Isabelle package, it should
already include properly setup executables for CVC3, E, SPASS, and Z3, ready to use.%
\footnote{Vampire's and Yices's licenses prevent us from doing the same for
these otherwise remarkable tools.}
For Z3, you must additionally set the variable
\texttt{Z3\_NON\_COMMERCIAL} to ``yes'' to confirm that you are a
noncommercial user, either in the environment in which Isabelle is
launched or in your
\texttt{\$ISABELLE\_HOME\_USER/etc/settings} file.

\item[\labelitemi] Alternatively, you can download the Isabelle-aware CVC3, E,
SPASS, and Z3 binary packages from \download. Extract the archives, then add a
line to your \texttt{\$ISABELLE\_HOME\_USER\slash etc\slash components}%
\footnote{The variable \texttt{\$ISABELLE\_HOME\_USER} is set by Isabelle at
startup. Its value can be retrieved by executing \texttt{isabelle}
\texttt{getenv} \texttt{ISABELLE\_HOME\_USER} on the command line.}
file with the absolute path to CVC3, E, SPASS, or Z3. For example, if the
\texttt{components} file does not exist yet and you extracted SPASS to
\texttt{/usr/local/spass-3.8ds}, create it with the single line

\prew
\texttt{/usr/local/spass-3.8ds}
\postw

in it.

\item[\labelitemi] If you prefer to build E, LEO-II, Satallax, or SPASS
manually, or found a Vampire executable somewhere (e.g.,
\url{http://www.vprover.org/}), set the environment variable \texttt{E\_HOME},
\texttt{LEO2\_HOME}, \texttt{SATALLAX\_HOME}, \texttt{SPASS\_HOME}, or
\texttt{VAMPIRE\_HOME} to the directory that contains the \texttt{eproof},
\texttt{leo}, \texttt{satallax}, \texttt{SPASS}, or \texttt{vampire} executable.
Sledgehammer has been tested with E 1.0 to 1.4, LEO-II 1.3.4, Satallax 2.2, 2.3,
and 2.4, SPASS 3.8ds, and Vampire 0.6, 1.0, and 1.8.%
\footnote{Following the rewrite of Vampire, the counter for version numbers was
reset to 0; hence the (new) Vampire versions 0.6, 1.0, and 1.8 are more recent
than 9.0 or 11.5.}%
Since the ATPs' output formats are neither documented nor stable, other
versions might not work well with Sledgehammer. Ideally,
you should also set \texttt{E\_VERSION}, \texttt{LEO2\_VERSION},
\texttt{SATALLAX\_VERSION}, \texttt{SPASS\_VERSION}, or
\texttt{VAMPIRE\_VERSION} to the prover's version number (e.g., ``1.4'').

Similarly, if you want to build Alt-Ergo or CVC3, or found a
Yices or Z3 executable somewhere (e.g.,
\url{http://yices.csl.sri.com/download.shtml} or
\url{http://research.microsoft.com/en-us/um/redmond/projects/z3/download.html}),
set the environment variable \texttt{CVC3\_\allowbreak SOLVER},
\texttt{YICES\_SOLVER}, or \texttt{Z3\_SOLVER} to the complete path of
the executable, \emph{including the file name}. Sledgehammer has been tested
with Alt-Ergo 0.93, CVC3 2.2 and 2.4.1, Yices 1.0.28 and 1.0.33, and Z3 3.0,
3.1, 3.2, and 4.0. Since the SMT solvers' output formats are somewhat unstable,
other versions of the solvers might not work well with Sledgehammer. Ideally,
also set \texttt{CVC3\_VERSION}, \texttt{YICES\_VERSION}, or
\texttt{Z3\_VERSION} to the solver's version number (e.g., ``4.0'').
\end{enum}
\end{sloppy}

To check whether E, SPASS, Vampire, and/or Z3 are successfully installed, try
out the example in \S\ref{first-steps}. If the remote versions of any of these
provers is used (identified by the prefix ``\emph{remote\_\/}''), or if the
local versions fail to solve the easy goal presented there, something must be
wrong with the installation.

Remote prover invocation requires Perl with the World Wide Web Library
(\texttt{libwww-perl}) installed. If you must use a proxy server to access the
Internet, set the \texttt{http\_proxy} environment variable to the proxy, either
in the environment in which Isabelle is launched or in your
\texttt{\$ISABELLE\_HOME\_USER/etc/settings} file. Here are a few
examples:

\prew
\texttt{http\_proxy=http://proxy.example.org} \\
\texttt{http\_proxy=http://proxy.example.org:8080} \\
\texttt{http\_proxy=http://joeblow:[e-mail]}
\postw

\section{First Steps}
\label{first-steps}

To illustrate Sledgehammer in context, let us start a theory file and
attempt to prove a simple lemma:

\prew
\textbf{theory}~\textit{Scratch} \\
\textbf{imports}~\textit{Main} \\
\textbf{begin} \\[2\smallskipamount]
%
\textbf{lemma} ``$[a] = [b] \,\Longrightarrow\, a = b$'' \\
\textbf{sledgehammer}
\postw

Instead of issuing the \textbf{sledgehammer} command, you can also find
Sledgehammer in the ``Commands'' submenu of the ``Isabelle'' menu in Proof
General or press the Emacs key sequence C-c C-a C-s.
Either way, Sledgehammer produces the following output after a few seconds:

\prew
\slshape
Sledgehammer: ``\textit{e\/}'' on goal \\
$[a] = [b] \,\Longrightarrow\, a = b$ \\
Try this: \textbf{by} (\textit{metis last\_ConsL}) (64 ms). \\[3\smallskipamount]
%
Sledgehammer: ``\textit{z3\/}'' on goal \\
$[a] = [b] \,\Longrightarrow\, a = b$ \\
Try this: \textbf{by} (\textit{metis list.inject}) (20 ms). \\[3\smallskipamount]
%
Sledgehammer: ``\textit{vampire\/}'' on goal \\
$[a] = [b] \,\Longrightarrow\, a = b$ \\
Try this: \textbf{by} (\textit{metis hd.simps}) (14 ms). \\[3\smallskipamount]
%
Sledgehammer: ``\textit{spass\/}'' on goal \\
$[a] = [b] \,\Longrightarrow\, a = b$ \\
Try this: \textbf{by} (\textit{metis list.inject}) (17 ms). \\[3\smallskipamount]
%
Sledgehammer: ``\textit{remote\_waldmeister\/}'' on goal \\
$[a] = [b] \,\Longrightarrow\, a = b$ \\
Try this: \textbf{by} (\textit{metis hd.simps}) (15 ms). \\[3\smallskipamount]
%
Sledgehammer: ``\textit{remote\_e\_sine\/}'' on goal \\
$[a] = [b] \,\Longrightarrow\, a = b$ \\
Try this: \textbf{by} (\textit{metis hd.simps}) (18 ms).
\postw

Sledgehammer ran E, E-SInE, SPASS, Vampire, Waldmeister, and Z3 in parallel.
Depending on which provers are installed and how many processor cores are
available, some of the provers might be missing or present with a
\textit{remote\_} prefix. Waldmeister is run only for unit equational problems,
where the goal's conclusion is a (universally quantified) equation.

For each successful prover, Sledgehammer gives a one-liner \textit{metis} or
\textit{smt} method call. Rough timings are shown in parentheses, indicating how
fast the call is. You can click the proof to insert it into the theory text.

In addition, you can ask Sledgehammer for an Isar text proof by passing the
\textit{isar\_proof} option (\S\ref{output-format}):

\prew
\textbf{sledgehammer} [\textit{isar\_proof}]
\postw

When Isar proof construction is successful, it can yield proofs that are more
readable and also faster than the \textit{metis} or \textit{smt} one-liners.
This feature is experimental and is only available for ATPs.

\section{Hints}
\label{hints}

This section presents a few hints that should help you get the most out of
Sledgehammer. Frequently asked questions are answered in
\S\ref{frequently-asked-questions}.

%\newcommand\point[1]{\medskip\par{\sl\bfseries#1}\par\nopagebreak}
\newcommand\point[1]{\subsection{\emph{#1}}}

\point{Presimplify the goal}

For best results, first simplify your problem by calling \textit{auto} or at
least \textit{safe} followed by \textit{simp\_all}. The SMT solvers provide
arithmetic decision procedures, but the ATPs typically do not (or if they do,
Sledgehammer does not use it yet). Apart from Waldmeister, they are not
especially good at heavy rewriting, but because they regard equations as
undirected, they often prove theorems that require the reverse orientation of a
\textit{simp} rule. Higher-order problems can be tackled, but the success rate
is better for first-order problems. Hence, you may get better results if you
first simplify the problem to remove higher-order features.

\point{Make sure E, SPASS, Vampire, and Z3 are locally installed}

Locally installed provers are faster and more reliable than those running on
servers. See \S\ref{installation} for details on how to install them.

\point{Familiarize yourself with the most important options}

Sledgehammer's options are fully documented in \S\ref{command-syntax}. Many of
the options are very specialized, but serious users of the tool should at least
familiarize themselves with the following options:

\begin{enum}
\item[\labelitemi] \textbf{\textit{provers}} (\S\ref{mode-of-operation}) specifies
the automatic provers (ATPs and SMT solvers) that should be run whenever
Sledgehammer is invoked (e.g., ``\textit{provers}~= \textit{e spass
remote\_vampire\/}''). For convenience, you can omit ``\textit{provers}~=''
and simply write the prover names as a space-separated list (e.g., ``\textit{e
spass remote\_vampire\/}'').

\item[\labelitemi] \textbf{\textit{max\_facts}} (\S\ref{relevance-filter})
specifies the maximum number of facts that should be passed to the provers. By
default, the value is prover-dependent but varies between about 50 and 1000. If
the provers time out, you can try lowering this value to, say, 25 or 50 and see
if that helps.

\item[\labelitemi] \textbf{\textit{isar\_proof}} (\S\ref{output-format}) specifies
that Isar proofs should be generated, instead of one-liner \textit{metis} or
\textit{smt} proofs. The length of the Isar proofs can be controlled by setting
\textit{isar\_shrink\_factor} (\S\ref{output-format}).

\item[\labelitemi] \textbf{\textit{timeout}} (\S\ref{timeouts}) controls the
provers' time limit. It is set to 30 seconds, but since Sledgehammer runs
asynchronously you should not hesitate to raise this limit to 60 or 120 seconds
if you are the kind of user who can think clearly while ATPs are active.
\end{enum}

Options can be set globally using \textbf{sledgehammer\_params}
(\S\ref{command-syntax}). The command also prints the list of all available
options with their current value. Fact selection can be influenced by specifying
``$(\textit{add}{:}~\textit{my\_facts})$'' after the \textbf{sledgehammer} call
to ensure that certain facts are included, or simply ``$(\textit{my\_facts})$''
to force Sledgehammer to run only with $\textit{my\_facts}$.

\section{Frequently Asked Questions}
\label{frequently-asked-questions}

This sections answers frequently (and infrequently) asked questions about
Sledgehammer. It is a good idea to skim over it now even if you do not have any
questions at this stage. And if you have any further questions not listed here,
send them to the author at \authoremail.

\point{Which facts are passed to the automatic provers?}

Sledgehammer heuristically selects a few hundred relevant lemmas from the
currently loaded libraries. The component that performs this selection is
called \emph{relevance filter}.

\begin{enum}
\item[\labelitemi]
The traditional relevance filter, called \emph{MePo}, assigns a score to every
available fact (lemma, theorem, definition, or axiom) based upon how many
constants that fact shares with the conjecture. This process iterates to include
facts relevant to those just accepted. The constants are weighted to give
unusual ones greater significance. MePo copes best when the conjecture contains
some unusual constants; if all the constants are common, it is unable to
discriminate among the hundreds of facts that are picked up. The filter is also
memoryless: It has no information about how many times a particular fact has
been used in a proof, and it cannot learn.

\item[\labelitemi]
An experimental, memoryful alternative to MePo is \emph{MaSh}
(\underline{Ma}chine Learner for \underline{S}ledge\underline{h}ammer). It
relies on an external tool called \texttt{mash} that applies machine learning to
the problem of finding relevant facts.

\item[\labelitemi] The \emph{Mesh} filter combines MePo and MaSh.
\end{enum}

The default is either MePo or Mesh, depending on whether \texttt{mash} is
installed and what class of provers the target prover belongs to
(\S\ref{relevance-filter}).

The number of facts included in a problem varies from prover to prover, since
some provers get overwhelmed more easily than others. You can show the number of
facts given using the \textit{verbose} option (\S\ref{output-format}) and the
actual facts using \textit{debug} (\S\ref{output-format}).

Sledgehammer is good at finding short proofs combining a handful of existing
lemmas. If you are looking for longer proofs, you must typically restrict the
number of facts, by setting the \textit{max\_facts} option
(\S\ref{relevance-filter}) to, say, 25 or 50.

You can also influence which facts are actually selected in a number of ways. If
you simply want to ensure that a fact is included, you can specify it using the
``$(\textit{add}{:}~\textit{my\_facts})$'' syntax. For example:
%
\prew
\textbf{sledgehammer} (\textit{add}: \textit{hd.simps} \textit{tl.simps})
\postw
%
The specified facts then replace the least relevant facts that would otherwise be
included; the other selected facts remain the same.
If you want to direct the selection in a particular direction, you can specify
the facts via \textbf{using}:
%
\prew
\textbf{using} \textit{hd.simps} \textit{tl.simps} \\
\textbf{sledgehammer}
\postw
%
The facts are then more likely to be selected than otherwise, and if they are
selected at iteration $j$ they also influence which facts are selected at
iterations $j + 1$, $j + 2$, etc. To give them even more weight, try
%
\prew
\textbf{using} \textit{hd.simps} \textit{tl.simps} \\
\textbf{apply}~\textbf{--} \\
\textbf{sledgehammer}
\postw

\point{Why does Metis fail to reconstruct the proof?}

There are many reasons. If Metis runs seemingly forever, that is a sign that the
proof is too difficult for it. Metis's search is complete, so it should
eventually find it, but that's little consolation. There are several possible
solutions:

\begin{enum}
\item[\labelitemi] Try the \textit{isar\_proof} option (\S\ref{output-format}) to
obtain a step-by-step Isar proof where each step is justified by \textit{metis}.
Since the steps are fairly small, \textit{metis} is more likely to be able to
replay them.

\item[\labelitemi] Try the \textit{smt} proof method instead of \textit{metis}. It
is usually stronger, but you need to either have Z3 available to replay the
proofs, trust the SMT solver, or use certificates. See the documentation in the
\emph{SMT} theory (\texttt{\$ISABELLE\_HOME/src/HOL/SMT.thy}) for details.

\item[\labelitemi] Try the \textit{blast} or \textit{auto} proof methods, passing
the necessary facts via \textbf{unfolding}, \textbf{using}, \textit{intro}{:},
\textit{elim}{:}, \textit{dest}{:}, or \textit{simp}{:}, as appropriate.
\end{enum}

In some rare cases, \textit{metis} fails fairly quickly, and you get the error
message

\prew
\slshape
One-line proof reconstruction failed.
\postw

This message indicates that Sledgehammer determined that the goal is provable,
but the proof is, for technical reasons, beyond \textit{metis}'s power. You can
then try again with the \textit{strict} option (\S\ref{problem-encoding}).

If the goal is actually unprovable and you did not specify an unsound encoding
using \textit{type\_enc} (\S\ref{problem-encoding}), this is a bug, and you are
strongly encouraged to report this to the author at \authoremail.

\point{Why are the generated Isar proofs so ugly/broken?}

The current implementation of the Isar proof feature,
enabled by the \textit{isar\_proof} option (\S\ref{output-format}),
is highly experimental. Work on a new implementation has begun. There is a large body of
research into transforming resolution proofs into natural deduction proofs (such
as Isar proofs), which we hope to leverage. In the meantime, a workaround is to
set the \textit{isar\_shrink\_factor} option (\S\ref{output-format}) to a larger
value or to try several provers and keep the nicest-looking proof.

\point{How can I tell whether a suggested proof is sound?}

Earlier versions of Sledgehammer often suggested unsound proofs---either proofs
of nontheorems or simply proofs that rely on type-unsound inferences. This
is a thing of the past, unless you explicitly specify an unsound encoding
using \textit{type\_enc} (\S\ref{problem-encoding}).
%
Officially, the only form of ``unsoundness'' that lurks in the sound
encodings is related to missing characteristic theorems of datatypes. For
example,

\prew
\textbf{lemma}~``$\exists \mathit{xs}.\; \mathit{xs} \neq []$'' \\
\textbf{sledgehammer} ()
\postw

suggests an argumentless \textit{metis} call that fails. However, the conjecture
does actually hold, and the \textit{metis} call can be repaired by adding
\textit{list.distinct}.
%
We hope to address this problem in a future version of Isabelle. In the
meantime, you can avoid it by passing the \textit{strict} option
(\S\ref{problem-encoding}).

\point{What are the \textit{full\_types}, \textit{no\_types}, and
\textit{mono\_tags} arguments to Metis?}

The \textit{metis}~(\textit{full\_types}) proof method
and its cousin \textit{metis}~(\textit{mono\_tags}) are fully-typed
version of Metis. It is somewhat slower than \textit{metis}, but the proof
search is fully typed, and it also includes more powerful rules such as the
axiom ``$x = \const{True} \mathrel{\lor} x = \const{False}$'' for reasoning in
higher-order places (e.g., in set comprehensions). The method kicks in
automatically as a fallback when \textit{metis} fails, and it is sometimes
generated by Sledgehammer instead of \textit{metis} if the proof obviously
requires type information or if \textit{metis} failed when Sledgehammer
preplayed the proof. (By default, Sledgehammer tries to run \textit{metis} with
various options for up to 3 seconds each time to ensure that the generated
one-line proofs actually work and to display timing information. This can be
configured using the \textit{preplay\_timeout} and \textit{dont\_preplay}
options (\S\ref{timeouts}).)
%
At the other end of the soundness spectrum, \textit{metis} (\textit{no\_types})
uses no type information at all during the proof search, which is more efficient
but often fails. Calls to \textit{metis} (\textit{no\_types}) are occasionally
generated by Sledgehammer.
%
See the \textit{type\_enc} option (\S\ref{problem-encoding}) for details.

Incidentally, if you ever see warnings such as

\prew
\slshape
Metis: Falling back on ``\textit{metis} (\textit{full\_types})''.
\postw

for a successful \textit{metis} proof, you can advantageously pass the
\textit{full\_types} option to \textit{metis} directly.

\point{And what are the \textit{lifting} and \textit{hide\_lams} arguments
to Metis?}

Orthogonally to the encoding of types, it is important to choose an appropriate
translation of $\lambda$-abstractions. Metis supports three translation schemes,
in decreasing order of power: Curry combinators (the default),
$\lambda$-lifting, and a ``hiding'' scheme that disables all reasoning under
$\lambda$-abstractions. The more powerful schemes also give the automatic
provers more rope to hang themselves. See the \textit{lam\_trans} option (\S\ref{problem-encoding}) for details.

\point{Are generated proofs minimal?}

Automatic provers frequently use many more facts than are necessary.
Sledgehammer inclues a minimization tool that takes a set of facts returned by a
given prover and repeatedly calls the same prover, \textit{metis}, or
\textit{smt} with subsets of those axioms in order to find a minimal set.
Reducing the number of axioms typically improves Metis's speed and success rate,
while also removing superfluous clutter from the proof scripts.

In earlier versions of Sledgehammer, generated proofs were systematically
accompanied by a suggestion to invoke the minimization tool. This step is now
performed implicitly if it can be done in a reasonable amount of time (something
that can be guessed from the number of facts in the original proof and the time
it took to find or preplay it).

In addition, some provers (e.g., Yices) do not provide proofs or sometimes
produce incomplete proofs. The minimizer is then invoked to find out which facts
are actually needed from the (large) set of facts that was initially given to
the prover. Finally, if a prover returns a proof with lots of facts, the
minimizer is invoked automatically since Metis would be unlikely to re-find the
proof.
%
Automatic minimization can be forced or disabled using the \textit{minimize}
option (\S\ref{mode-of-operation}).

\point{A strange error occurred---what should I do?}

Sledgehammer tries to give informative error messages. Please report any strange
error to the author at \authoremail. This applies double if you get the message

\prew
\slshape
The prover found a type-unsound proof involving ``\textit{foo\/}'',
``\textit{bar\/}'', and ``\textit{baz\/}'' even though a supposedly type-sound
encoding was used (or, less likely, your axioms are inconsistent). You might
want to report this to the Isabelle developers.
\postw

\point{Auto can solve it---why not Sledgehammer?}

Problems can be easy for \textit{auto} and difficult for automatic provers, but
the reverse is also true, so do not be discouraged if your first attempts fail.
Because the system refers to all theorems known to Isabelle, it is particularly
suitable when your goal has a short proof from lemmas that you do not know
about.

\point{Why are there so many options?}

Sledgehammer's philosophy should work out of the box, without user guidance.
Many of the options are meant to be used mostly by the Sledgehammer developers
for experimentation purposes. Of course, feel free to experiment with them if
you are so inclined.

\section{Command Syntax}
\label{command-syntax}

\subsection{Sledgehammer}

Sledgehammer can be invoked at any point when there is an open goal by entering
the \textbf{sledgehammer} command in the theory file. Its general syntax is as
follows:

\prew
\textbf{sledgehammer} \qty{subcommand}$^?$ \qty{options}$^?$ \qty{facts\_override}$^?$ \qty{num}$^?$
\postw

For convenience, Sledgehammer is also available in the ``Commands'' submenu of
the ``Isabelle'' menu in Proof General or by pressing the Emacs key sequence C-c
C-a C-s. This is equivalent to entering the \textbf{sledgehammer} command with
no arguments in the theory text.

In the general syntax, the \qty{subcommand} may be any of the following:

\begin{enum}
\item[\labelitemi] \textbf{\textit{run} (the default):} Runs Sledgehammer on
subgoal number \qty{num} (1 by default), with the given options and facts.

\item[\labelitemi] \textbf{\textit{min}:} Attempts to minimize the facts
specified in the \qty{facts\_override} argument to obtain a simpler proof
involving fewer facts. The options and goal number are as for \textit{run}.

\item[\labelitemi] \textbf{\textit{messages}:} Redisplays recent messages issued
by Sledgehammer. This allows you to examine results that might have been lost
due to Sledgehammer's asynchronous nature. The \qty{num} argument specifies a
limit on the number of messages to display (10 by default).

\item[\labelitemi] \textbf{\textit{supported\_provers}:} Prints the list of
automatic provers supported by Sledgehammer. See \S\ref{installation} and
\S\ref{mode-of-operation} for more information on how to install automatic
provers.

\item[\labelitemi] \textbf{\textit{running\_provers}:} Prints information about
currently running automatic provers, including elapsed runtime and remaining
time until timeout.

\item[\labelitemi] \textbf{\textit{kill\_provers}:} Terminates all running
automatic provers.

\item[\labelitemi] \textbf{\textit{unlearn}:} Resets the MaSh machine learner,
erasing any persistent state.

\item[\labelitemi] \textbf{\textit{learn}:} Invokes the MaSh machine learner on
the current theory to process all the available facts. This happens
automatically at Sledgehammer invocations if the \textit{learn} option
(\S\ref{relevance-filter}) is enabled.

\item[\labelitemi] \textbf{\textit{relearn}:} Same as \textit{unlearn} followed
by \textit{learn}.

\item[\labelitemi] \textbf{\textit{running\_learners}:} Prints information about
currently running machine learners, including elapsed runtime and remaining
time until timeout.

\item[\labelitemi] \textbf{\textit{kill\_learners}:} Terminates all running
machine learners.

\item[\labelitemi] \textbf{\textit{refresh\_tptp}:} Refreshes the list of remote
ATPs available at System\-On\-TPTP \cite{sutcliffe-2000}.
\end{enum}

Sledgehammer's behavior can be influenced by various \qty{options}, which can be
specified in brackets after the \textbf{sledgehammer} command. The
\qty{options} are a list of key--value pairs of the form ``[$k_1 = v_1,
\ldots, k_n = v_n$]''. For Boolean options, ``= \textit{true\/}'' is optional. For
example:

\prew
\textbf{sledgehammer} [\textit{isar\_proof}, \,\textit{timeout} = 120]
\postw

Default values can be set using \textbf{sledgehammer\_\allowbreak params}:

\prew
\textbf{sledgehammer\_params} \qty{options}
\postw

The supported options are described in \S\ref{option-reference}.

The \qty{facts\_override} argument lets you alter the set of facts that go
through the relevance filter. It may be of the form ``(\qty{facts})'', where
\qty{facts} is a space-separated list of Isabelle facts (theorems, local
assumptions, etc.), in which case the relevance filter is bypassed and the given
facts are used. It may also be of the form ``(\textit{add}:\ \qty{facts\/_{\mathrm{1}}})'',
``(\textit{del}:\ \qty{facts\/_{\mathrm{2}}})'', or ``(\textit{add}:\ \qty{facts\/_{\mathrm{1}}}\
\textit{del}:\ \qty{facts\/_{\mathrm{2}}})'', where the relevance filter is instructed to
proceed as usual except that it should consider \qty{facts\/_{\mathrm{1}}}
highly-relevant and \qty{facts\/_{\mathrm{2}}} fully irrelevant.

You can instruct Sledgehammer to run automatically on newly entered theorems by
enabling the ``Auto Sledgehammer'' option in Proof General's ``Isabelle'' menu.
For automatic runs, only the first prover set using \textit{provers}
(\S\ref{mode-of-operation}) is considered, fewer facts are passed to the prover,
\textit{slice} (\S\ref{mode-of-operation}) is disabled, \textit{strict}
(\S\ref{problem-encoding}) is enabled, \textit{verbose} (\S\ref{output-format})
and \textit{debug} (\S\ref{output-format}) are disabled, and \textit{timeout}
(\S\ref{timeouts}) is superseded by the ``Auto Tools Time Limit'' in Proof
General's ``Isabelle'' menu. Sledgehammer's output is also more concise.

\subsection{Metis}

The \textit{metis} proof method has the syntax

\prew
\textbf{\textit{metis}}~(\qty{options})${}^?$~\qty{facts}${}^?$
\postw

where \qty{facts} is a list of arbitrary facts and \qty{options} is a
comma-separated list consisting of at most one $\lambda$ translation scheme
specification with the same semantics as Sledgehammer's \textit{lam\_trans}
option (\S\ref{problem-encoding}) and at most one type encoding specification
with the same semantics as Sledgehammer's \textit{type\_enc} option
(\S\ref{problem-encoding}).
%
The supported $\lambda$ translation schemes are \textit{hide\_lams},
\textit{lifting}, and \textit{combs} (the default).
%
All the untyped type encodings listed in \S\ref{problem-encoding} are supported.
For convenience, the following aliases are provided:
\begin{enum}
\item[\labelitemi] \textbf{\textit{full\_types}:} Synonym for \textit{poly\_guards\_query}.
\item[\labelitemi] \textbf{\textit{partial\_types}:} Synonym for \textit{poly\_args}.
\item[\labelitemi] \textbf{\textit{no\_types}:} Synonym for \textit{erased}.
\end{enum}

\section{Option Reference}
\label{option-reference}

\def\defl{\{}
\def\defr{\}}

\def\flushitem#1{\item[]\noindent\kern-\leftmargin \textbf{#1}}
\def\optrueonly#1{\flushitem{\textit{#1} $\bigl[$= \textit{true}$\bigr]$\enskip}\nopagebreak\\[\parskip]}
\def\optrue#1#2{\flushitem{\textit{#1} $\bigl[$= \qtybf{bool}$\bigr]$\enskip \defl\textit{true}\defr\hfill (neg.: \textit{#2})}\nopagebreak\\[\parskip]}
\def\opfalse#1#2{\flushitem{\textit{#1} $\bigl[$= \qtybf{bool}$\bigr]$\enskip \defl\textit{false}\defr\hfill (neg.: \textit{#2})}\nopagebreak\\[\parskip]}
\def\opsmart#1#2{\flushitem{\textit{#1} $\bigl[$= \qtybf{smart\_bool}$\bigr]$\enskip \defl\textit{smart}\defr\hfill (neg.: \textit{#2})}\nopagebreak\\[\parskip]}
\def\opsmartx#1#2{\flushitem{\textit{#1} $\bigl[$= \qtybf{smart\_bool}$\bigr]$\enskip \defl\textit{smart}\defr\\\hbox{}\hfill (neg.: \textit{#2})}\nopagebreak\\[\parskip]}
\def\opnodefault#1#2{\flushitem{\textit{#1} = \qtybf{#2}} \nopagebreak\\[\parskip]}
\def\opnodefaultbrk#1#2{\flushitem{$\bigl[$\textit{#1} =$\bigr]$ \qtybf{#2}} \nopagebreak\\[\parskip]}
\def\opdefault#1#2#3{\flushitem{\textit{#1} = \qtybf{#2}\enskip \defl\textit{#3}\defr} \nopagebreak\\[\parskip]}
\def\oparg#1#2#3{\flushitem{\textit{#1} \qtybf{#2} = \qtybf{#3}} \nopagebreak\\[\parskip]}
\def\opargbool#1#2#3{\flushitem{\textit{#1} \qtybf{#2} $\bigl[$= \qtybf{bool}$\bigr]$\hfill (neg.: \textit{#3})}\nopagebreak\\[\parskip]}
\def\opargboolorsmart#1#2#3{\flushitem{\textit{#1} \qtybf{#2} $\bigl[$= \qtybf{smart\_bool}$\bigr]$\hfill (neg.: \textit{#3})}\nopagebreak\\[\parskip]}

Sledgehammer's options are categorized as follows:\ mode of operation
(\S\ref{mode-of-operation}), problem encoding (\S\ref{problem-encoding}),
relevance filter (\S\ref{relevance-filter}), output format
(\S\ref{output-format}), authentication (\S\ref{authentication}), and timeouts
(\S\ref{timeouts}).

The descriptions below refer to the following syntactic quantities:

\begin{enum}
\item[\labelitemi] \qtybf{string}: A string.
\item[\labelitemi] \qtybf{bool\/}: \textit{true} or \textit{false}.
\item[\labelitemi] \qtybf{smart\_bool\/}: \textit{true}, \textit{false}, or
\textit{smart}.
\item[\labelitemi] \qtybf{int\/}: An integer.
%\item[\labelitemi] \qtybf{float\/}: A floating-point number (e.g., 2.5).
\item[\labelitemi] \qtybf{float\_pair\/}: A pair of floating-point numbers
(e.g., 0.6 0.95).
\item[\labelitemi] \qtybf{smart\_int\/}: An integer or \textit{smart}.
\item[\labelitemi] \qtybf{float\_or\_none\/}: A floating-point number (e.g., 60 or
0.5) expressing a number of seconds, or the keyword \textit{none} ($\infty$
seconds).
\end{enum}

Default values are indicated in curly brackets (\textrm{\{\}}). Boolean options
have a negative counterpart (e.g., \textit{blocking} vs.\
\textit{non\_blocking}). When setting Boolean options or their negative
counterparts, ``= \textit{true\/}'' may be omitted.

\subsection{Mode of Operation}
\label{mode-of-operation}

\begin{enum}
\opnodefaultbrk{provers}{string}
Specifies the automatic provers to use as a space-separated list (e.g.,
``\textit{e}~\textit{spass}~\textit{remote\_vampire\/}'').
Provers can be run locally or remotely; see \S\ref{installation} for
installation instructions.

The following local provers are supported:

\begin{enum}
\item[\labelitemi] \textbf{\textit{alt\_ergo}:} Alt-Ergo is a polymorphic
SMT solver developed by Bobot et al.\ \cite{alt-ergo}.
It supports the TPTP polymorphic typed first-order format (TFF1) via Why3
\cite{why3}. It is included for experimental purposes. To use Alt-Ergo, set the
environment variable \texttt{WHY3\_HOME} to the directory that contains the
\texttt{why3} executable. Sledgehammer has been tested with Alt-Ergo 0.93 and an
unidentified development version of Why3.

\item[\labelitemi] \textbf{\textit{cvc3}:} CVC3 is an SMT solver developed by
Clark Barrett, Cesare Tinelli, and their colleagues \cite{cvc3}. To use CVC3,
set the environment variable \texttt{CVC3\_SOLVER} to the complete path of the
executable, including the file name, or install the prebuilt CVC3 package from
\download. Sledgehammer has been tested with version 2.2 and 2.4.1.

\item[\labelitemi] \textbf{\textit{e}:} E is a first-order resolution prover
developed by Stephan Schulz \cite{schulz-2002}. To use E, set the environment
variable \texttt{E\_HOME} to the directory that contains the \texttt{eproof}
executable and \texttt{E\_VERSION} to the version number (e.g., ``1.4''), or
install the prebuilt E package from \download. Sledgehammer has been tested with
versions 1.0 to 1.4.

\item[\labelitemi] \textbf{\textit{leo2}:} LEO-II is an automatic
higher-order prover developed by Christoph Benzm\"uller et al.\ \cite{leo2},
with support for the TPTP typed higher-order syntax (THF0). To use LEO-II, set
the environment variable \texttt{LEO2\_HOME} to the directory that contains the
\texttt{leo} executable. Sledgehammer requires version 1.2.9 or above.

\item[\labelitemi] \textbf{\textit{metis}:} Although it is much less powerful than
the external provers, Metis itself can be used for proof search.

\item[\labelitemi] \textbf{\textit{satallax}:} Satallax is an automatic
higher-order prover developed by Chad Brown et al.\ \cite{satallax}, with
support for the TPTP typed higher-order syntax (THF0). To use Satallax, set the
environment variable \texttt{SATALLAX\_HOME} to the directory that contains the
\texttt{satallax} executable. Sledgehammer requires version 2.2 or above.

\item[\labelitemi] \textbf{\textit{smt}:} The \textit{smt} proof method with the
current settings (usually:\ Z3 with proof reconstruction).

\item[\labelitemi] \textbf{\textit{spass}:} SPASS is a first-order resolution
prover developed by Christoph Weidenbach et al.\ \cite{weidenbach-et-al-2009}.
To use SPASS, set the environment variable \texttt{SPASS\_HOME} to the directory
that contains the \texttt{SPASS} executable and \texttt{SPASS\_VERSION} to the
version number (e.g., ``3.8ds''), or install the prebuilt SPASS package from
\download. Sledgehammer requires version 3.8ds or above.

\item[\labelitemi] \textbf{\textit{vampire}:} Vampire is a first-order resolution
prover developed by Andrei Voronkov and his colleagues
\cite{riazanov-voronkov-2002}. To use Vampire, set the environment variable
\texttt{VAMPIRE\_HOME} to the directory that contains the \texttt{vampire}
executable and \texttt{VAMPIRE\_VERSION} to the version number (e.g.,
``1.8rev1435''). Sledgehammer has been tested with versions 0.6, 1.0, and 1.8.
Versions strictly above 1.8 (e.g., ``1.8rev1435'') support the TPTP typed
first-order format (TFF0).

\item[\labelitemi] \textbf{\textit{yices}:} Yices is an SMT solver developed at
SRI \cite{yices}. To use Yices, set the environment variable
\texttt{YICES\_SOLVER} to the complete path of the executable, including the
file name. Sledgehammer has been tested with version 1.0.28.

\item[\labelitemi] \textbf{\textit{z3}:} Z3 is an SMT solver developed at
Microsoft Research \cite{z3}. To use Z3, set the environment variable
\texttt{Z3\_SOLVER} to the complete path of the executable, including the file
name, and set \texttt{Z3\_NON\_COMMERCIAL} to ``yes'' to confirm that you are a
noncommercial user. Sledgehammer has been tested with versions 3.0, 3.1, 3.2,
and 4.0.

\item[\labelitemi] \textbf{\textit{z3\_tptp}:} This version of Z3 pretends to be
an ATP, exploiting Z3's support for the TPTP untyped and typed first-order
formats (FOF and TFF0). It is included for experimental purposes. It
requires version 3.0 or above. To use it, set the environment variable
\texttt{Z3\_HOME} to the directory that contains the \texttt{z3}
executable.
\end{enum}

The following remote provers are supported:

\begin{enum}
\item[\labelitemi] \textbf{\textit{remote\_cvc3}:} The remote version of CVC3 runs
on servers at the TU M\"unchen (or wherever \texttt{REMOTE\_SMT\_URL} is set to
point).

\item[\labelitemi] \textbf{\textit{remote\_e}:} The remote version of E runs
on Geoff Sutcliffe's Miami servers \cite{sutcliffe-2000}.

\item[\labelitemi] \textbf{\textit{remote\_e\_sine}:} E-SInE is a metaprover
developed by Kry\v stof Hoder \cite{sine} based on E. It runs on Geoff
Sutcliffe's Miami servers.

\item[\labelitemi] \textbf{\textit{remote\_e\_tofof}:} E-ToFoF is a metaprover
developed by Geoff Sutcliffe \cite{tofof} based on E running on his Miami
servers. This ATP supports the TPTP typed first-order format (TFF0). The
remote version of E-ToFoF runs on Geoff Sutcliffe's Miami servers.

\item[\labelitemi] \textbf{\textit{remote\_iprover}:} iProver is a pure
instantiation-based prover developed by Konstantin Korovin \cite{korovin-2009}. The
remote version of iProver runs on Geoff Sutcliffe's Miami servers
\cite{sutcliffe-2000}.

\item[\labelitemi] \textbf{\textit{remote\_iprover\_eq}:} iProver-Eq is an
instantiation-based prover with native support for equality developed by
Konstantin Korovin and Christoph Sticksel \cite{korovin-sticksel-2010}. The
remote version of iProver-Eq runs on Geoff Sutcliffe's Miami servers
\cite{sutcliffe-2000}.

\item[\labelitemi] \textbf{\textit{remote\_leo2}:} The remote version of LEO-II
runs on Geoff Sutcliffe's Miami servers \cite{sutcliffe-2000}.

\item[\labelitemi] \textbf{\textit{remote\_satallax}:} The remote version of
Satallax runs on Geoff Sutcliffe's Miami servers \cite{sutcliffe-2000}.

\item[\labelitemi] \textbf{\textit{remote\_snark}:} SNARK is a first-order
resolution prover developed by Stickel et al.\ \cite{snark}. It supports the
TPTP typed first-order format (TFF0). The remote version of SNARK runs on
Geoff Sutcliffe's Miami servers.

\item[\labelitemi] \textbf{\textit{remote\_vampire}:} The remote version of
Vampire runs on Geoff Sutcliffe's Miami servers.

\item[\labelitemi] \textbf{\textit{remote\_waldmeister}:} Waldmeister is a unit
equality prover developed by Hillenbrand et al.\ \cite{waldmeister}. It can be
used to prove universally quantified equations using unconditional equations,
corresponding to the TPTP CNF UEQ division. The remote version of Waldmeister
runs on Geoff Sutcliffe's Miami servers.

\item[\labelitemi] \textbf{\textit{remote\_z3}:} The remote version of Z3 runs on
servers at the TU M\"unchen (or wherever \texttt{REMOTE\_SMT\_URL} is set to
point).

\item[\labelitemi] \textbf{\textit{remote\_z3\_tptp}:} The remote version of ``Z3
with TPTP syntax'' runs on Geoff Sutcliffe's Miami servers.
\end{enum}

By default, Sledgehammer runs E, E-SInE, SPASS, Vampire, Z3 (or whatever
the SMT module's \textit{smt\_solver} configuration option is set to), and (if
appropriate) Waldmeister in parallel---either locally or remotely, depending on
the number of processor cores available. For historical reasons, the default
value of this option can be overridden using the option ``Sledgehammer:
Provers'' in Proof General's ``Isabelle'' menu.

It is generally a good idea to run several provers in parallel. Running E,
SPASS, and Vampire for 5~seconds yields a similar success rate to running the
most effective of these for 120~seconds \cite{boehme-nipkow-2010}.

For the \textit{min} subcommand, the default prover is \textit{metis}. If
several provers are set, the first one is used.

\opnodefault{prover}{string}
Alias for \textit{provers}.

\opfalse{blocking}{non\_blocking}
Specifies whether the \textbf{sledgehammer} command should operate
synchronously. The asynchronous (non-blocking) mode lets the user start proving
the putative theorem manually while Sledgehammer looks for a proof, but it can
also be more confusing. Irrespective of the value of this option, Sledgehammer
is always run synchronously for the new jEdit-based user interface or if
\textit{debug} (\S\ref{output-format}) is enabled.

\optrue{slice}{dont\_slice}
Specifies whether the time allocated to a prover should be sliced into several
segments, each of which has its own set of possibly prover-dependent options.
For SPASS and Vampire, the first slice tries the fast but incomplete
set-of-support (SOS) strategy, whereas the second slice runs without it. For E,
up to three slices are tried, with different weighted search strategies and
number of facts. For SMT solvers, several slices are tried with the same options
each time but fewer and fewer facts. According to benchmarks with a timeout of
30 seconds, slicing is a valuable optimization, and you should probably leave it
enabled unless you are conducting experiments. This option is implicitly
disabled for (short) automatic runs.

\nopagebreak
{\small See also \textit{verbose} (\S\ref{output-format}).}

\opsmart{minimize}{dont\_minimize}
Specifies whether the minimization tool should be invoked automatically after
proof search. By default, automatic minimization takes place only if
it can be done in a reasonable amount of time (as determined by
the number of facts in the original proof and the time it took to find or
preplay it) or the proof involves an unreasonably large number of facts.

\nopagebreak
{\small See also \textit{preplay\_timeout} (\S\ref{timeouts})
and \textit{dont\_preplay} (\S\ref{timeouts}).}

\opfalse{overlord}{no\_overlord}
Specifies whether Sledgehammer should put its temporary files in
\texttt{\$ISA\-BELLE\_\allowbreak HOME\_\allowbreak USER}, which is useful for
debugging Sledgehammer but also unsafe if several instances of the tool are run
simultaneously. The files are identified by the prefix \texttt{prob\_}; you may
safely remove them after Sledgehammer has run.

\nopagebreak
{\small See also \textit{debug} (\S\ref{output-format}).}
\end{enum}

\subsection{Relevance Filter}
\label{relevance-filter}

\begin{enum}
\opdefault{max\_facts}{smart\_int}{smart}
Specifies the maximum number of facts that may be returned by the relevance
filter. If the option is set to \textit{smart}, it is set to a value that was
empirically found to be appropriate for the prover. Typical values range between
50 and 1000.

\opdefault{fact\_thresholds}{float\_pair}{\upshape 0.45~0.85}
Specifies the thresholds above which facts are considered relevant by the
relevance filter. The first threshold is used for the first iteration of the
relevance filter and the second threshold is used for the last iteration (if it
is reached). The effective threshold is quadratically interpolated for the other
iterations. Each threshold ranges from 0 to 1, where 0 means that all theorems
are relevant and 1 only theorems that refer to previously seen constants.

\opdefault{max\_new\_mono\_instances}{int}{smart}
Specifies the maximum number of monomorphic instances to generate beyond
\textit{max\_facts}. The higher this limit is, the more monomorphic instances
are potentially generated. Whether monomorphization takes place depends on the
type encoding used. If the option is set to \textit{smart}, it is set to a value
that was empirically found to be appropriate for the prover. For most provers,
this value is 200.

\nopagebreak
{\small See also \textit{type\_enc} (\S\ref{problem-encoding}).}

\opdefault{max\_mono\_iters}{int}{smart}
Specifies the maximum number of iterations for the monomorphization fixpoint
construction. The higher this limit is, the more monomorphic instances are
potentially generated. Whether monomorphization takes place depends on the
type encoding used. If the option is set to \textit{smart}, it is set to a value
that was empirically found to be appropriate for the prover. For most provers,
this value is 3.

\nopagebreak
{\small See also \textit{type\_enc} (\S\ref{problem-encoding}).}
\end{enum}

\subsection{Problem Encoding}
\label{problem-encoding}

\newcommand\comb[1]{\const{#1}}

\begin{enum}
\opdefault{lam\_trans}{string}{smart}
Specifies the $\lambda$ translation scheme to use in ATP problems. The supported
translation schemes are listed below:

\begin{enum}
\item[\labelitemi] \textbf{\textit{hide\_lams}:} Hide the $\lambda$-abstractions
by replacing them by unspecified fresh constants, effectively disabling all
reasoning under $\lambda$-abstractions.

\item[\labelitemi] \textbf{\textit{lifting}:} Introduce a new
supercombinator \const{c} for each cluster of $n$~$\lambda$-abstractions,
defined using an equation $\const{c}~x_1~\ldots~x_n = t$ ($\lambda$-lifting).

\item[\labelitemi] \textbf{\textit{combs}:} Rewrite lambdas to the Curry
combinators (\comb{I}, \comb{K}, \comb{S}, \comb{B}, \comb{C}). Combinators
enable the ATPs to synthesize $\lambda$-terms but tend to yield bulkier formulas
than $\lambda$-lifting: The translation is quadratic in the worst case, and the
equational definitions of the combinators are very prolific in the context of
resolution.

\item[\labelitemi] \textbf{\textit{combs\_and\_lifting}:} Introduce a new
supercombinator \const{c} for each cluster of $\lambda$-abstractions and characterize it both using a
lifted equation $\const{c}~x_1~\ldots~x_n = t$ and via Curry combinators.

\item[\labelitemi] \textbf{\textit{combs\_or\_lifting}:} For each cluster of
$\lambda$-abstractions, heuristically choose between $\lambda$-lifting and Curry
combinators.

\item[\labelitemi] \textbf{\textit{keep\_lams}:}
Keep the $\lambda$-abstractions in the generated problems. This is available
only with provers that support the THF0 syntax.

\item[\labelitemi] \textbf{\textit{smart}:} The actual translation scheme used
depends on the ATP and should be the most efficient scheme for that ATP.
\end{enum}

For SMT solvers, the $\lambda$ translation scheme is always \textit{lifting},
irrespective of the value of this option.

\opsmartx{uncurried\_aliases}{no\_uncurried\_aliases}
Specifies whether fresh function symbols should be generated as aliases for
applications of curried functions in ATP problems.

\opdefault{type\_enc}{string}{smart}
Specifies the type encoding to use in ATP problems. Some of the type encodings
are unsound, meaning that they can give rise to spurious proofs
(unreconstructible using \textit{metis}). The type encodings are
listed below, with an indication of their soundness in parentheses.
An asterisk (*) indicates that the encoding is slightly incomplete for
reconstruction with \textit{metis}, unless the \emph{strict} option (described
below) is enabled.

\begin{enum}
\item[\labelitemi] \textbf{\textit{erased} (unsound):} No type information is
supplied to the ATP, not even to resolve overloading. Types are simply erased.

\item[\labelitemi] \textbf{\textit{poly\_guards} (sound):} Types are encoded using
a predicate \const{g}$(\tau, t)$ that guards bound
variables. Constants are annotated with their types, supplied as extra
arguments, to resolve overloading.

\item[\labelitemi] \textbf{\textit{poly\_tags} (sound):} Each term and subterm is
tagged with its type using a function $\const{t\/}(\tau, t)$.

\item[\labelitemi] \textbf{\textit{poly\_args} (unsound):}
Like for \textit{poly\_guards} constants are annotated with their types to
resolve overloading, but otherwise no type information is encoded. This
is the default encoding used by the \textit{metis} command.

\item[\labelitemi]
\textbf{%
\textit{raw\_mono\_guards}, \textit{raw\_mono\_tags} (sound); \\
\textit{raw\_mono\_args} (unsound):} \\
Similar to \textit{poly\_guards}, \textit{poly\_tags}, and \textit{poly\_args},
respectively, but the problem is additionally monomorphized, meaning that type
variables are instantiated with heuristically chosen ground types.
Monomorphization can simplify reasoning but also leads to larger fact bases,
which can slow down the ATPs.

\item[\labelitemi]
\textbf{%
\textit{mono\_guards}, \textit{mono\_tags} (sound);
\textit{mono\_args} (unsound):} \\
Similar to
\textit{raw\_mono\_guards}, \textit{raw\_mono\_tags}, and
\textit{raw\_mono\_args}, respectively but types are mangled in constant names
instead of being supplied as ground term arguments. The binary predicate
$\const{g}(\tau, t)$ becomes a unary predicate
$\const{g\_}\tau(t)$, and the binary function
$\const{t}(\tau, t)$ becomes a unary function
$\const{t\_}\tau(t)$.

\item[\labelitemi] \textbf{\textit{mono\_native} (sound):} Exploits native
first-order types if the prover supports the TFF0, TFF1, or THF0 syntax;
otherwise, falls back on \textit{mono\_guards}. The problem is monomorphized.

\item[\labelitemi] \textbf{\textit{mono\_native\_higher} (sound):} Exploits
native higher-order types if the prover supports the THF0 syntax; otherwise,
falls back on \textit{mono\_native} or \textit{mono\_guards}. The problem is
monomorphized.

\item[\labelitemi] \textbf{\textit{poly\_native} (sound):} Exploits native
first-order polymorphic types if the prover supports the TFF1 syntax; otherwise,
falls back on \textit{mono\_native}.

\item[\labelitemi]
\textbf{%
\textit{poly\_guards}?, \textit{poly\_tags}?, \textit{raw\_mono\_guards}?, \\
\textit{raw\_mono\_tags}?, \textit{mono\_guards}?, \textit{mono\_tags}?, \\
\textit{mono\_native}? (sound*):} \\
The type encodings \textit{poly\_guards}, \textit{poly\_tags},
\textit{raw\_mono\_guards}, \textit{raw\_mono\_tags}, \textit{mono\_guards},
\textit{mono\_tags}, and \textit{mono\_native} are fully typed and sound. For
each of these, Sledgehammer also provides a lighter variant identified by a
question mark (`\hbox{?}')\ that detects and erases monotonic types, notably
infinite types. (For \textit{mono\_native}, the types are not actually erased
but rather replaced by a shared uniform type of individuals.) As argument to the
\textit{metis} proof method, the question mark is replaced by a
\hbox{``\textit{\_query\/}''} suffix.

\item[\labelitemi]
\textbf{%
\textit{poly\_guards}??, \textit{poly\_tags}??, \textit{raw\_mono\_guards}??, \\
\textit{raw\_mono\_tags}??, \textit{mono\_guards}??, \textit{mono\_tags}?? \\
(sound*):} \\
Even lighter versions of the `\hbox{?}' encodings. As argument to the
\textit{metis} proof method, the `\hbox{??}' suffix is replaced by
\hbox{``\textit{\_query\_query\/}''}.

\item[\labelitemi]
\textbf{%
\textit{poly\_guards}@, \textit{poly\_tags}@, \textit{raw\_mono\_guards}@, \\
\textit{raw\_mono\_tags}@ (sound*):} \\
Alternative versions of the `\hbox{??}' encodings. As argument to the
\textit{metis} proof method, the `\hbox{@}' suffix is replaced by
\hbox{``\textit{\_at\/}''}.

\item[\labelitemi] \textbf{\textit{poly\_args}?, \textit{raw\_mono\_args}? (unsound):} \\
Lighter versions of \textit{poly\_args} and \textit{raw\_mono\_args}.

\item[\labelitemi] \textbf{\textit{smart}:} The actual encoding used depends on
the ATP and should be the most efficient sound encoding for that ATP.
\end{enum}

For SMT solvers, the type encoding is always \textit{mono\_native}, irrespective
of the value of this option.

\nopagebreak
{\small See also \textit{max\_new\_mono\_instances} (\S\ref{relevance-filter})
and \textit{max\_mono\_iters} (\S\ref{relevance-filter}).}

\opfalse{strict}{non\_strict}
Specifies whether Sledgehammer should run in its strict mode. In that mode,
sound type encodings marked with an asterisk (*) above are made complete
for reconstruction with \textit{metis}, at the cost of some clutter in the
generated problems. This option has no effect if \textit{type\_enc} is
deliberately set to an unsound encoding.
\end{enum}

\subsection{Output Format}
\label{output-format}

\begin{enum}

\opfalse{verbose}{quiet}
Specifies whether the \textbf{sledgehammer} command should explain what it does.
This option is implicitly disabled for automatic runs.

\opfalse{debug}{no\_debug}
Specifies whether Sledgehammer should display additional debugging information
beyond what \textit{verbose} already displays. Enabling \textit{debug} also
enables \textit{verbose} and \textit{blocking} (\S\ref{mode-of-operation})
behind the scenes. The \textit{debug} option is implicitly disabled for
automatic runs.

\nopagebreak
{\small See also \textit{overlord} (\S\ref{mode-of-operation}).}

\opfalse{isar\_proof}{no\_isar\_proof}
Specifies whether Isar proofs should be output in addition to one-liner
\textit{metis} proofs. Isar proof construction is still experimental and often
fails; however, they are usually faster and sometimes more robust than
\textit{metis} proofs.

\opdefault{isar\_shrink\_factor}{int}{\upshape 1}
Specifies the granularity of the Isar proof. A value of $n$ indicates that each
Isar proof step should correspond to a group of up to $n$ consecutive proof
steps in the ATP proof.
\end{enum}

\subsection{Authentication}
\label{authentication}

\begin{enum}
\opnodefault{expect}{string}
Specifies the expected outcome, which must be one of the following:

\begin{enum}
\item[\labelitemi] \textbf{\textit{some}:} Sledgehammer found a proof.
\item[\labelitemi] \textbf{\textit{none}:} Sledgehammer found no proof.
\item[\labelitemi] \textbf{\textit{timeout}:} Sledgehammer timed out.
\item[\labelitemi] \textbf{\textit{unknown}:} Sledgehammer encountered some
problem.
\end{enum}

Sledgehammer emits an error (if \textit{blocking} is enabled) or a warning
(otherwise) if the actual outcome differs from the expected outcome. This option
is useful for regression testing.

\nopagebreak
{\small See also \textit{blocking} (\S\ref{mode-of-operation}) and
\textit{timeout} (\S\ref{timeouts}).}
\end{enum}

\subsection{Timeouts}
\label{timeouts}

\begin{enum}
\opdefault{timeout}{float\_or\_none}{\upshape 30}
Specifies the maximum number of seconds that the automatic provers should spend
searching for a proof. This excludes problem preparation and is a soft limit.
For historical reasons, the default value of this option can be overridden using
the option ``Sledgehammer: Time Limit'' in Proof General's ``Isabelle'' menu.

\opdefault{preplay\_timeout}{float\_or\_none}{\upshape 3}
Specifies the maximum number of seconds that \textit{metis} or \textit{smt}
should spend trying to ``preplay'' the found proof. If this option is set to 0,
no preplaying takes place, and no timing information is displayed next to the
suggested \textit{metis} calls.

\nopagebreak
{\small See also \textit{minimize} (\S\ref{mode-of-operation}).}

\optrueonly{dont\_preplay}
Alias for ``\textit{preplay\_timeout} = 0''.

\end{enum}

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\end{document}