find-theorems.md

Using find_theorems effectively

This command is for searching for theorems. If you are looking for a constant/function instead, look at find_consts.

There is an introduction to the find_theorems command in the Isabelle/HOL tutorial. Here we cover some additional material and useful patterns.

find_theorems can be written in the theory as a diagnostic command, or accessed from the jEdit Query panel. Sometimes it is useful to create a "New Floating Instance" of the panel to view theorems while you work.

As a reminder, the basic search criteria are:

syntax	matches
"pattern"	only theorems that match this pattern
name: "string"	only theorems whose names contain this string
simp: "pattern"	equations that can rewrite this pattern
intro, elim, dest, solves	theorems that are intro/elim/dest rules for the current proof goal, or solve the goal
- <criterion>	only theorems that do not match the criterion

Patterns

find_theorems attempts to match your pattern(s) in theorems. Usually, using dummy terms (underscores) is enough. Sometimes it pays to be more creative.

Match the conclusion of a theorem

The query

"if _ then _ else _"

returns many kinds of theorems. If we are only interested in theorems with this exact conclusion, write

"_ ⟹ if _ then _ else _"

You can also use the same trick to match assumptions:

"if _ then _ else _ ⟹ _"

Be aware that these won't match theorems with no assumptions! Alternatively, write a pattern of type prop, so that it matches only assumptions and conclusions:

"Trueprop (if _ then _ else _)"

Finding theorems for a type

Suppose we want to find nat division rules:

"_ div _"

That wasn't very effective. Use type annotations to narrow the search:

"_ div _ :: nat"

Using dummy types to find word division rules:

"_ div _ :: _ word"

Don't be too specific

Terms and types can be too specific and prevent useful results from being returned. In the previous example, generic division rules are not returned by the queries with type constraints. We can search for generic rules separately:

name:ring_div_class "_ div _"

This fetches theorems proved in the locales ring_div_class and semiring_div_class.

In the previous example, we deliberately added the type constraint. More often, the cause is a subterm of the pattern that is too concrete. For example,

"my_const + _ = _ + my_const"

is unlikely to return any results. When this happens, try again with a more general query that replaces my_const.

Using schematics

Schematic variables can appear multiple times --- use this to your advantage. Suppose we wanted a commutativity rule for my_const + _ (previous section):

"_ + _ = _ + _"

But we get many irrelevant results. Instead, use named schematics:

"?x + ?y = ?y + ?x"

Note that schematics in multiple patterns are matched independently, even if they have the same name, so this technique becomes less effective.

Names

Many theorems are organised into theories and locales. When you have a pattern that's too general and it's not clear how to refine it, names can be used as "thematic" search criteria.

Find simp rules for bytes:

name:"simp" "_ :: 8 word"

Find induction rules in the List theory:

name:"List." name:induct

Note the "." after "List". Adding or removing dots can have a great effect on some queries, e.g. find simp rules not defined by the datatype package:

name:"simp" -name:".simp" "_ :: 8 word"

One problem with our List query is that not all induction rules are contained in List. Instead, we can search for a conclusion that is common to list induction rules:

name:induct "_ ⟹ _ (_ :: _ list)"

Indeed, we see that other theories also have list induction rules.

The name search criterion is often useful with negation. For instance

name:induct "_ ⟹ _ (_ :: _ list)" -name: "List."

will remove everything from the List theory from the previous search.

Finally, a note on the pattern "_ (_ :: _ list)" that we used to match the conclusion. find_theorems requires every dummy term or schematic to match something in the theorem, which is different from how unification of schematics usually behaves (e.g. in apply rule). We exploit this to match only theorems whose conclusions talk about a list.