-- Mathlib.Tactic.Simps.Basic
/-- The `@[simps]` attribute automatically derives lemmas specifying the projections of this
declaration.

Example:
```lean
@[simps] def foo : ℕ × ℤ := (1, 2)
```
derives two `simp` lemmas:
```lean
@[simp] lemma foo_fst : foo.fst = 1
@[simp] lemma foo_snd : foo.snd = 2
```

* It does not derive `simp` lemmas for the prop-valued projections.
* It will automatically reduce newly created beta-redexes, but will not unfold any definitions.
* If the structure has a coercion to either sorts or functions, and this is defined to be one
  of the projections, then this coercion will be used instead of the projection.
* If the structure is a class that has an instance to a notation class, like `Neg` or `Mul`,
  then this notation is used instead of the corresponding projection.
* You can specify custom projections, by giving a declaration with name
  `{StructureName}.Simps.{projectionName}`. See Note [custom simps projection].

  Example:
  ```lean
  def Equiv.Simps.invFun (e : α ≃ β) : β → α := e.symm
  @[simps] def Equiv.trans (e₁ : α ≃ β) (e₂ : β ≃ γ) : α ≃ γ :=
  ⟨e₂ ∘ e₁, e₁.symm ∘ e₂.symm⟩
  ```
  generates
  ```
  @[simp] lemma Equiv.trans_toFun : ∀ {α β γ} (e₁ e₂) (a : α), ⇑(e₁.trans e₂) a = (⇑e₂ ∘ ⇑e₁) a
  @[simp] lemma Equiv.trans_invFun : ∀ {α β γ} (e₁ e₂) (a : γ),
    ⇑((e₁.trans e₂).symm) a = (⇑(e₁.symm) ∘ ⇑(e₂.symm)) a
  ```

* You can specify custom projection names, by specifying the new projection names using
  `initialize_simps_projections`.
  Example: `initialize_simps_projections Equiv (toFun → apply, invFun → symm_apply)`.
  See `initialize_simps_projections` for more information.

* If one of the fields itself is a structure, this command will recursively create
  `simp` lemmas for all fields in that structure.
  * Exception: by default it will not recursively create `simp` lemmas for fields in the structures
    `Prod`, `PProd`, and `Opposite`. You can give explicit projection names or change the value of
    `Simps.Config.notRecursive` to override this behavior.

  Example:
  ```lean
  structure MyProd (α β : Type*) := (fst : α) (snd : β)
  @[simps] def foo : Prod ℕ ℕ × MyProd ℕ ℕ := ⟨⟨1, 2⟩, 3, 4⟩
  ```
  generates
  ```lean
  @[simp] lemma foo_fst : foo.fst = (1, 2)
  @[simp] lemma foo_snd_fst : foo.snd.fst = 3
  @[simp] lemma foo_snd_snd : foo.snd.snd = 4
  ```

* You can use `@[simps proj1 proj2 ...]` to only generate the projection lemmas for the specified
  projections.
* Recursive projection names can be specified using `proj1_proj2_proj3`.
  This will create a lemma of the form `foo.proj1.proj2.proj3 = ...`.

  Example:
  ```lean
  structure MyProd (α β : Type*) := (fst : α) (snd : β)
  @[simps fst fst_fst snd] def foo : Prod ℕ ℕ × MyProd ℕ ℕ := ⟨⟨1, 2⟩, 3, 4⟩
  ```
  generates
  ```lean
  @[simp] lemma foo_fst : foo.fst = (1, 2)
  @[simp] lemma foo_fst_fst : foo.fst.fst = 1
  @[simp] lemma foo_snd : foo.snd = {fst := 3, snd := 4}
  ```
* If one of the values is an eta-expanded structure, we will eta-reduce this structure.

  Example:
  ```lean
  structure EquivPlusData (α β) extends α ≃ β where
    data : Bool
  @[simps] def EquivPlusData.rfl {α} : EquivPlusData α α := { Equiv.refl α with data := true }
  ```
  generates the following:
  ```lean
  @[simp] lemma bar_toEquiv : ∀ {α : Sort*}, bar.toEquiv = Equiv.refl α
  @[simp] lemma bar_data : ∀ {α : Sort*}, bar.data = true
  ```
  This is true, even though Lean inserts an eta-expanded version of `Equiv.refl α` in the
  definition of `bar`.
* You can add additional attributes to all lemmas generated by `simps` using e.g.
  `@[simps (attr := grind =)]`.
* For configuration options, see the doc string of `Simps.Config`.
* The precise syntax is `simps config ident*`, where `config` declares configuration options,
  and `ident*` is a list of desired projection names.
  The `config` can contain `(attr := a)` entries, where `a` is a list of attributes.
* Configuration options can be given using `(config := e)` where `e : Simps.Config`,
  or by specifying options directly, like `-fullyApplied` or `(notRecursive := [])`.
* `@[simps]` reduces let-expressions where necessary.
* When option `trace.simps.verbose` is true, `simps` will print the projections it finds and the
  lemmas it generates. The same can be achieved by using `@[simps?]`.
* Use `@[to_additive (attr := simps)]` to apply both `to_additive` and `simps` to a definition
  This will also generate the additive versions of all `simp` lemmas.
 -/
Lean.Parser.Attr.simps : Lean.ParserDescr