simp 属性将声明添加到默认 simp 集。
如果该声明是定义，则将该定义标记为待展开；如果是定理，则将该定理注册为重写规则。
attr ::= ...
| Theorems tagged with the `simp` attribute are used by the simplifier
(i.e., the `simp` tactic, and its variants) to simplify expressions occurring in your goals.
We call theorems tagged with the `simp` attribute "simp theorems" or "simp lemmas".
Lean maintains a database/index containing all active simp theorems.
Here is an example of a simp theorem.
```lean
@[simp] theorem ne_eq (a b : α) : (a ≠ b) = Not (a = b) := rfl
```
This simp theorem instructs the simplifier to replace instances of the term
`a ≠ b` (e.g. `x + 0 ≠ y`) with `Not (a = b)` (e.g., `Not (x + 0 = y)`).
The simplifier applies simp theorems in one direction only:
if `A = B` is a simp theorem, then `simp` replaces `A`s with `B`s,
but it doesn't replace `B`s with `A`s. Hence a simp theorem should have the
property that its right-hand side is "simpler" than its left-hand side.
In particular, `=` and `↔` should not be viewed as symmetric operators in this situation.
The following would be a terrible simp theorem (if it were even allowed):
```lean
@[simp] lemma mul_right_inv_bad (a : G) : 1 = a * a⁻¹ := ...
```
Replacing 1 with a * a⁻¹ is not a sensible default direction to travel.
Even worse would be a theorem that causes expressions to grow without bound,
causing simp to loop forever.
By default the simplifier applies `simp` theorems to an expression `e`
after its sub-expressions have been simplified.
We say it performs a bottom-up simplification.
You can instruct the simplifier to apply a theorem before its sub-expressions
have been simplified by using the modifier `↓`. Here is an example
```lean
@[simp↓] theorem not_and_eq (p q : Prop) : (¬ (p ∧ q)) = (¬p ∨ ¬q) :=
```
You can instruct the simplifier to rewrite the lemma from right-to-left:
```lean
attribute @[simp ←] and_assoc
```
When multiple simp theorems are applicable, the simplifier uses the one with highest priority.
The equational theorems of functions are applied at very low priority (100 and below).
If there are several with the same priority, it is uses the "most recent one". Example:
```lean
@[simp high] theorem cond_true (a b : α) : cond true a b = a := rfl
@[simp low+1] theorem or_true (p : Prop) : (p ∨ True) = True :=
propext <| Iff.intro (fun _ => trivial) (fun _ => Or.inr trivial)
@[simp 100] theorem ite_self {d : Decidable c} (a : α) : ite c a a = a := by
cases d <;> rfl
```
attr ::= ... |simpTheorems tagged with the `simp` attribute are used by the simplifier (i.e., the `simp` tactic, and its variants) to simplify expressions occurring in your goals. We call theorems tagged with the `simp` attribute "simp theorems" or "simp lemmas". Lean maintains a database/index containing all active simp theorems. Here is an example of a simp theorem. ```lean @[simp] theorem ne_eq (a b : α) : (a ≠ b) = Not (a = b) := rfl ``` This simp theorem instructs the simplifier to replace instances of the term `a ≠ b` (e.g. `x + 0 ≠ y`) with `Not (a = b)` (e.g., `Not (x + 0 = y)`). The simplifier applies simp theorems in one direction only: if `A = B` is a simp theorem, then `simp` replaces `A`s with `B`s, but it doesn't replace `B`s with `A`s. Hence a simp theorem should have the property that its right-hand side is "simpler" than its left-hand side. In particular, `=` and `↔` should not be viewed as symmetric operators in this situation. The following would be a terrible simp theorem (if it were even allowed): ```lean @[simp] lemma mul_right_inv_bad (a : G) : 1 = a * a⁻¹ := ... ``` Replacing 1 with a * a⁻¹ is not a sensible default direction to travel. Even worse would be a theorem that causes expressions to grow without bound, causing simp to loop forever. By default the simplifier applies `simp` theorems to an expression `e` after its sub-expressions have been simplified. We say it performs a bottom-up simplification. You can instruct the simplifier to apply a theorem before its sub-expressions have been simplified by using the modifier `↓`. Here is an example ```lean @[simp↓] theorem not_and_eq (p q : Prop) : (¬ (p ∧ q)) = (¬p ∨ ¬q) := ``` You can instruct the simplifier to rewrite the lemma from right-to-left: ```lean attribute @[simp ←] and_assoc ``` When multiple simp theorems are applicable, the simplifier uses the one with highest priority. The equational theorems of functions are applied at very low priority (100 and below). If there are several with the same priority, it is uses the "most recent one". Example: ```lean @[simp high] theorem cond_true (a b : α) : cond true a b = a := rfl @[simp low+1] theorem or_true (p : Prop) : (p ∨ True) = True := propext <| Iff.intro (fun _ => trivial) (fun _ => Or.inr trivial) @[simp 100] theorem ite_self {d : Decidable c} (a : α) : ite c a a = a := by cases d <;> rfl ```↑ prio?Use this rewrite rule after entering the subterms
attr ::= ... |simpTheorems tagged with the `simp` attribute are used by the simplifier (i.e., the `simp` tactic, and its variants) to simplify expressions occurring in your goals. We call theorems tagged with the `simp` attribute "simp theorems" or "simp lemmas". Lean maintains a database/index containing all active simp theorems. Here is an example of a simp theorem. ```lean @[simp] theorem ne_eq (a b : α) : (a ≠ b) = Not (a = b) := rfl ``` This simp theorem instructs the simplifier to replace instances of the term `a ≠ b` (e.g. `x + 0 ≠ y`) with `Not (a = b)` (e.g., `Not (x + 0 = y)`). The simplifier applies simp theorems in one direction only: if `A = B` is a simp theorem, then `simp` replaces `A`s with `B`s, but it doesn't replace `B`s with `A`s. Hence a simp theorem should have the property that its right-hand side is "simpler" than its left-hand side. In particular, `=` and `↔` should not be viewed as symmetric operators in this situation. The following would be a terrible simp theorem (if it were even allowed): ```lean @[simp] lemma mul_right_inv_bad (a : G) : 1 = a * a⁻¹ := ... ``` Replacing 1 with a * a⁻¹ is not a sensible default direction to travel. Even worse would be a theorem that causes expressions to grow without bound, causing simp to loop forever. By default the simplifier applies `simp` theorems to an expression `e` after its sub-expressions have been simplified. We say it performs a bottom-up simplification. You can instruct the simplifier to apply a theorem before its sub-expressions have been simplified by using the modifier `↓`. Here is an example ```lean @[simp↓] theorem not_and_eq (p q : Prop) : (¬ (p ∧ q)) = (¬p ∨ ¬q) := ``` You can instruct the simplifier to rewrite the lemma from right-to-left: ```lean attribute @[simp ←] and_assoc ``` When multiple simp theorems are applicable, the simplifier uses the one with highest priority. The equational theorems of functions are applied at very low priority (100 and below). If there are several with the same priority, it is uses the "most recent one". Example: ```lean @[simp high] theorem cond_true (a b : α) : cond true a b = a := rfl @[simp low+1] theorem or_true (p : Prop) : (p ∨ True) = True := propext <| Iff.intro (fun _ => trivial) (fun _ => Or.inr trivial) @[simp 100] theorem ite_self {d : Decidable c} (a : α) : ite c a a = a := by cases d <;> rfl ```↓ prio?Use this rewrite rule before entering the subterms
attr ::= ...
| Theorems tagged with the `simp` attribute are used by the simplifier
(i.e., the `simp` tactic, and its variants) to simplify expressions occurring in your goals.
We call theorems tagged with the `simp` attribute "simp theorems" or "simp lemmas".
Lean maintains a database/index containing all active simp theorems.
Here is an example of a simp theorem.
```lean
@[simp] theorem ne_eq (a b : α) : (a ≠ b) = Not (a = b) := rfl
```
This simp theorem instructs the simplifier to replace instances of the term
`a ≠ b` (e.g. `x + 0 ≠ y`) with `Not (a = b)` (e.g., `Not (x + 0 = y)`).
The simplifier applies simp theorems in one direction only:
if `A = B` is a simp theorem, then `simp` replaces `A`s with `B`s,
but it doesn't replace `B`s with `A`s. Hence a simp theorem should have the
property that its right-hand side is "simpler" than its left-hand side.
In particular, `=` and `↔` should not be viewed as symmetric operators in this situation.
The following would be a terrible simp theorem (if it were even allowed):
```lean
@[simp] lemma mul_right_inv_bad (a : G) : 1 = a * a⁻¹ := ...
```
Replacing 1 with a * a⁻¹ is not a sensible default direction to travel.
Even worse would be a theorem that causes expressions to grow without bound,
causing simp to loop forever.
By default the simplifier applies `simp` theorems to an expression `e`
after its sub-expressions have been simplified.
We say it performs a bottom-up simplification.
You can instruct the simplifier to apply a theorem before its sub-expressions
have been simplified by using the modifier `↓`. Here is an example
```lean
@[simp↓] theorem not_and_eq (p q : Prop) : (¬ (p ∧ q)) = (¬p ∨ ¬q) :=
```
You can instruct the simplifier to rewrite the lemma from right-to-left:
```lean
attribute @[simp ←] and_assoc
```
When multiple simp theorems are applicable, the simplifier uses the one with highest priority.
The equational theorems of functions are applied at very low priority (100 and below).
If there are several with the same priority, it is uses the "most recent one". Example:
```lean
@[simp high] theorem cond_true (a b : α) : cond true a b = a := rfl
@[simp low+1] theorem or_true (p : Prop) : (p ∨ True) = True :=
propext <| Iff.intro (fun _ => trivial) (fun _ => Or.inr trivial)
@[simp 100] theorem ite_self {d : Decidable c} (a : α) : ite c a a = a := by
cases d <;> rfl
```