File: Mathlib/Algebra/Field/Defs.lean

full_name: NNRat.castRec
code: /-- The default definition of the coercion `ℚ≥0 → K` for a division semiring `K`.

`↑q : K` is defined as `(q.num : K) / (q.den : K)`.

Do not use this directly (instances of `DivisionSemiring` are allowed to override that default for
better definitional properties). Instead, use the coercion. -/
def NNRat.castRec [NatCast K] [Div K] (q : ℚ≥0) : K 
goal: K

full_name: Rat.castRec
code: /-- The default definition of the coercion `ℚ → K` for a division ring `K`.

`↑q : K` is defined as `(q.num : K) / (q.den : K)`.

Do not use this directly (instances of `DivisionRing` are allowed to override that default for
better definitional properties). Instead, use the coercion. -/
def Rat.castRec [NatCast K] [IntCast K] [Div K] (q : ℚ) : K 
goal: K

full_name: DivisionSemiring
code: /-- A `DivisionSemiring` is a `Semiring` with multiplicative inverses for nonzero elements.

An instance of `DivisionSemiring K` includes maps `nnratCast : ℚ≥0 → K` and `nnqsmul : ℚ≥0 → K → K`.
Those two fields are needed to implement the `DivisionSemiring K → Algebra ℚ≥0 K` instance since we
need to control the specific definitions for some special cases of `K` (in particular `K = ℚ≥0`
itself). See also note [forgetful inheritance].

If the division semiring has positive characteristic `p`, our division by zero convention forces
`nnratCast (1 / p) = 1 / 0 = 0`. -/
class DivisionSemiring (α : Type*) extends Semiring α, GroupWithZero α, NNRatCast α where
  protected nnratCast := NNRat.castRec
  /-- However `NNRat.cast` is defined, it must be propositionally equal to `a / b`.

  Do not use this lemma directly. Use `NNRat.cast_def` instead. -/
  protected nnratCast_def (q : ℚ≥0) : (NNRat.cast q : α) = q.num / q.den := by intros; rfl
  /-- Scalar multiplication by a nonnegative rational number.

  Unless there is a risk of a `Module ℚ≥0 _` instance diamond, write `nnqsmul := _`. This will set
  `nnqsmul` to `(NNRat.cast · * ·)` thanks to unification in the default proof of `nnqsmul_def`.

  Do not use directly. Instead use the `•` notation. -/
  protected nnqsmul : ℚ≥0 → α → α
  /-- However `qsmul` is defined, it must be propositionally equal to multiplication by `Rat.cast`.

  Do not use this lemma directly. Use `NNRat.smul_def` instead. -/
  protected nnqsmul_def (q : ℚ≥0) (a : α) : nnqsmul q a = NNRat.cast q * a := by intros; rfl
goal: Type u_4

full_name: DivisionSemiring.nnqsmul_def
code: /-- A `DivisionSemiring` is a `Semiring` with multiplicative inverses for nonzero elements.

An instance of `DivisionSemiring K` includes maps `nnratCast : ℚ≥0 → K` and `nnqsmul : ℚ≥0 → K → K`.
Those two fields are needed to implement the `DivisionSemiring K → Algebra ℚ≥0 K` instance since we
need to control the specific definitions for some special cases of `K` (in particular `K = ℚ≥0`
itself). See also note [forgetful inheritance].

If the division semiring has positive characteristic `p`, our division by zero convention forces
`nnratCast (1 / p) = 1 / 0 = 0`. -/
class DivisionSemiring (α : Type*) extends Semiring α, GroupWithZero α, NNRatCast α where
  protected nnratCast := NNRat.castRec
  /-- However `NNRat.cast` is defined, it must be propositionally equal to `a / b`.

  Do not use this lemma directly. Use `NNRat.cast_def` instead. -/
  protected nnratCast_def (q : ℚ≥0) : (NNRat.cast q : α) = q.num / q.den := by intros; rfl
  /-- Scalar multiplication by a nonnegative rational number.

  Unless there is a risk of a `Module ℚ≥0 _` instance diamond, write `nnqsmul := _`. This will set
  `nnqsmul` to `(NNRat.cast · * ·)` thanks to unification in the default proof of `nnqsmul_def`.

  Do not use directly. Instead use the `•` notation. -/
  protected nnqsmul : ℚ≥0 → α → α
  /-- However `qsmul` is defined, it must be propositionally equal to multiplication by `Rat.cast`.

  Do not use this lemma directly. Use `NNRat.smul_def` instead. -/
  protected nnqsmul_def (q : ℚ≥0) (a : α) : nnqsmul q a = NNRat.cast q * a := by intros; rfl
goal: DivisionSemiring.nnqsmul q a = ↑q * a

full_name: DivisionSemiring.nnratCast_def
code: /-- A `DivisionSemiring` is a `Semiring` with multiplicative inverses for nonzero elements.

An instance of `DivisionSemiring K` includes maps `nnratCast : ℚ≥0 → K` and `nnqsmul : ℚ≥0 → K → K`.
Those two fields are needed to implement the `DivisionSemiring K → Algebra ℚ≥0 K` instance since we
need to control the specific definitions for some special cases of `K` (in particular `K = ℚ≥0`
itself). See also note [forgetful inheritance].

If the division semiring has positive characteristic `p`, our division by zero convention forces
`nnratCast (1 / p) = 1 / 0 = 0`. -/
class DivisionSemiring (α : Type*) extends Semiring α, GroupWithZero α, NNRatCast α where
  protected nnratCast := NNRat.castRec
  /-- However `NNRat.cast` is defined, it must be propositionally equal to `a / b`.

  Do not use this lemma directly. Use `NNRat.cast_def` instead. -/
  protected nnratCast_def (q : ℚ≥0) : (NNRat.cast q : α) = q.num / q.den := by intros; rfl
  /-- Scalar multiplication by a nonnegative rational number.

  Unless there is a risk of a `Module ℚ≥0 _` instance diamond, write `nnqsmul := _`. This will set
  `nnqsmul` to `(NNRat.cast · * ·)` thanks to unification in the default proof of `nnqsmul_def`.

  Do not use directly. Instead use the `•` notation. -/
  protected nnqsmul : ℚ≥0 → α → α
  /-- However `qsmul` is defined, it must be propositionally equal to multiplication by `Rat.cast`.

  Do not use this lemma directly. Use `NNRat.smul_def` instead. -/
  protected nnqsmul_def (q : ℚ≥0) (a : α) : nnqsmul q a = NNRat.cast q * a := by intros; rfl
goal: ↑q = ↑q.num / ↑q.den

full_name: DivisionSemiring.nnqsmul
code: /-- A `DivisionSemiring` is a `Semiring` with multiplicative inverses for nonzero elements.

An instance of `DivisionSemiring K` includes maps `nnratCast : ℚ≥0 → K` and `nnqsmul : ℚ≥0 → K → K`.
Those two fields are needed to implement the `DivisionSemiring K → Algebra ℚ≥0 K` instance since we
need to control the specific definitions for some special cases of `K` (in particular `K = ℚ≥0`
itself). See also note [forgetful inheritance].

If the division semiring has positive characteristic `p`, our division by zero convention forces
`nnratCast (1 / p) = 1 / 0 = 0`. -/
class DivisionSemiring (α : Type*) extends Semiring α, GroupWithZero α, NNRatCast α where
  protected nnratCast := NNRat.castRec
  /-- However `NNRat.cast` is defined, it must be propositionally equal to `a / b`.

  Do not use this lemma directly. Use `NNRat.cast_def` instead. -/
  protected nnratCast_def (q : ℚ≥0) : (NNRat.cast q : α) = q.num / q.den := by intros; rfl
  /-- Scalar multiplication by a nonnegative rational number.

  Unless there is a risk of a `Module ℚ≥0 _` instance diamond, write `nnqsmul := _`. This will set
  `nnqsmul` to `(NNRat.cast · * ·)` thanks to unification in the default proof of `nnqsmul_def`.

  Do not use directly. Instead use the `•` notation. -/
  protected nnqsmul : ℚ≥0 → α → α
  /-- However `qsmul` is defined, it must be propositionally equal to multiplication by `Rat.cast`.

  Do not use this lemma directly. Use `NNRat.smul_def` instead. -/
  protected nnqsmul_def (q : ℚ≥0) (a : α) : nnqsmul q a = NNRat.cast q * a := by intros; rfl
goal: ℚ≥0 → α → α

full_name: DivisionRing.inv_zero
code: /-- A `DivisionRing` is a `Ring` with multiplicative inverses for nonzero elements.

An instance of `DivisionRing K` includes maps `ratCast : ℚ → K` and `qsmul : ℚ → K → K`.
Those two fields are needed to implement the `DivisionRing K → Algebra ℚ K` instance since we need
to control the specific definitions for some special cases of `K` (in particular `K = ℚ` itself).
See also note [forgetful inheritance]. Similarly, there are maps `nnratCast ℚ≥0 → K` and
`nnqsmul : ℚ≥0 → K → K` to implement the `DivisionSemiring K → Algebra ℚ≥0 K` instance.

If the division ring has positive characteristic `p`, our division by zero convention forces
`ratCast (1 / p) = 1 / 0 = 0`. -/
class DivisionRing (α : Type*)
  extends Ring α, DivInvMonoid α, Nontrivial α, NNRatCast α, RatCast α where
  /-- For a nonzero `a`, `a⁻¹` is a right multiplicative inverse. -/
  protected mul_inv_cancel : ∀ (a : α), a ≠ 0 → a * a⁻¹ = 1
  /-- The inverse of `0` is `0` by convention. -/
  protected inv_zero : (0 : α)⁻¹ = 0
  protected nnratCast := NNRat.castRec
  /-- However `NNRat.cast` is defined, it must be equal to `a / b`.

  Do not use this lemma directly. Use `NNRat.cast_def` instead. -/
  protected nnratCast_def (q : ℚ≥0) : (NNRat.cast q : α) = q.num / q.den := by intros; rfl
  /-- Scalar multiplication by a nonnegative rational number.

  Unless there is a risk of a `Module ℚ≥0 _` instance diamond, write `nnqsmul := _`. This will set
  `nnqsmul` to `(NNRat.cast · * ·)` thanks to unification in the default proof of `nnqsmul_def`.

  Do not use directly. Instead use the `•` notation. -/
  protected nnqsmul : ℚ≥0 → α → α
  /-- However `qsmul` is defined, it must be propositionally equal to multiplication by `Rat.cast`.

  Do not use this lemma directly. Use `NNRat.smul_def` instead. -/
  protected nnqsmul_def (q : ℚ≥0) (a : α) : nnqsmul q a = NNRat.cast q * a := by intros; rfl
  protected ratCast := Rat.castRec
  /-- However `Rat.cast q` is defined, it must be propositionally equal to `q.num / q.den`.

  Do not use this lemma directly. Use `Rat.cast_def` instead. -/
  protected ratCast_def (q : ℚ) : (Rat.cast q : α) = q.num / q.den := by intros; rfl
  /-- Scalar multiplication by a rational number.

  Unless there is a risk of a `Module ℚ _` instance diamond, write `qsmul := _`. This will set
  `qsmul` to `(Rat.cast · * ·)` thanks to unification in the default proof of `qsmul_def`.

  Do not use directly. Instead use the `•` notation. -/
  protected qsmul : ℚ → α → α
  /-- However `qsmul` is defined, it must be propositionally equal to multiplication by `Rat.cast`.

  Do not use this lemma directly. Use `Rat.cast_def` instead. -/
  protected qsmul_def (a : ℚ) (x : α) : qsmul a x = Rat.cast a * x := by intros; rfl
goal: 0⁻¹ = 0

full_name: DivisionRing.nnqsmul
code: /-- A `DivisionRing` is a `Ring` with multiplicative inverses for nonzero elements.

An instance of `DivisionRing K` includes maps `ratCast : ℚ → K` and `qsmul : ℚ → K → K`.
Those two fields are needed to implement the `DivisionRing K → Algebra ℚ K` instance since we need
to control the specific definitions for some special cases of `K` (in particular `K = ℚ` itself).
See also note [forgetful inheritance]. Similarly, there are maps `nnratCast ℚ≥0 → K` and
`nnqsmul : ℚ≥0 → K → K` to implement the `DivisionSemiring K → Algebra ℚ≥0 K` instance.

If the division ring has positive characteristic `p`, our division by zero convention forces
`ratCast (1 / p) = 1 / 0 = 0`. -/
class DivisionRing (α : Type*)
  extends Ring α, DivInvMonoid α, Nontrivial α, NNRatCast α, RatCast α where
  /-- For a nonzero `a`, `a⁻¹` is a right multiplicative inverse. -/
  protected mul_inv_cancel : ∀ (a : α), a ≠ 0 → a * a⁻¹ = 1
  /-- The inverse of `0` is `0` by convention. -/
  protected inv_zero : (0 : α)⁻¹ = 0
  protected nnratCast := NNRat.castRec
  /-- However `NNRat.cast` is defined, it must be equal to `a / b`.

  Do not use this lemma directly. Use `NNRat.cast_def` instead. -/
  protected nnratCast_def (q : ℚ≥0) : (NNRat.cast q : α) = q.num / q.den := by intros; rfl
  /-- Scalar multiplication by a nonnegative rational number.

  Unless there is a risk of a `Module ℚ≥0 _` instance diamond, write `nnqsmul := _`. This will set
  `nnqsmul` to `(NNRat.cast · * ·)` thanks to unification in the default proof of `nnqsmul_def`.

  Do not use directly. Instead use the `•` notation. -/
  protected nnqsmul : ℚ≥0 → α → α
  /-- However `qsmul` is defined, it must be propositionally equal to multiplication by `Rat.cast`.

  Do not use this lemma directly. Use `NNRat.smul_def` instead. -/
  protected nnqsmul_def (q : ℚ≥0) (a : α) : nnqsmul q a = NNRat.cast q * a := by intros; rfl
  protected ratCast := Rat.castRec
  /-- However `Rat.cast q` is defined, it must be propositionally equal to `q.num / q.den`.

  Do not use this lemma directly. Use `Rat.cast_def` instead. -/
  protected ratCast_def (q : ℚ) : (Rat.cast q : α) = q.num / q.den := by intros; rfl
  /-- Scalar multiplication by a rational number.

  Unless there is a risk of a `Module ℚ _` instance diamond, write `qsmul := _`. This will set
  `qsmul` to `(Rat.cast · * ·)` thanks to unification in the default proof of `qsmul_def`.

  Do not use directly. Instead use the `•` notation. -/
  protected qsmul : ℚ → α → α
  /-- However `qsmul` is defined, it must be propositionally equal to multiplication by `Rat.cast`.

  Do not use this lemma directly. Use `Rat.cast_def` instead. -/
  protected qsmul_def (a : ℚ) (x : α) : qsmul a x = Rat.cast a * x := by intros; rfl
goal: ℚ≥0 → α → α

full_name: DivisionRing.qsmul_def
code: /-- A `DivisionRing` is a `Ring` with multiplicative inverses for nonzero elements.

An instance of `DivisionRing K` includes maps `ratCast : ℚ → K` and `qsmul : ℚ → K → K`.
Those two fields are needed to implement the `DivisionRing K → Algebra ℚ K` instance since we need
to control the specific definitions for some special cases of `K` (in particular `K = ℚ` itself).
See also note [forgetful inheritance]. Similarly, there are maps `nnratCast ℚ≥0 → K` and
`nnqsmul : ℚ≥0 → K → K` to implement the `DivisionSemiring K → Algebra ℚ≥0 K` instance.

If the division ring has positive characteristic `p`, our division by zero convention forces
`ratCast (1 / p) = 1 / 0 = 0`. -/
class DivisionRing (α : Type*)
  extends Ring α, DivInvMonoid α, Nontrivial α, NNRatCast α, RatCast α where
  /-- For a nonzero `a`, `a⁻¹` is a right multiplicative inverse. -/
  protected mul_inv_cancel : ∀ (a : α), a ≠ 0 → a * a⁻¹ = 1
  /-- The inverse of `0` is `0` by convention. -/
  protected inv_zero : (0 : α)⁻¹ = 0
  protected nnratCast := NNRat.castRec
  /-- However `NNRat.cast` is defined, it must be equal to `a / b`.

  Do not use this lemma directly. Use `NNRat.cast_def` instead. -/
  protected nnratCast_def (q : ℚ≥0) : (NNRat.cast q : α) = q.num / q.den := by intros; rfl
  /-- Scalar multiplication by a nonnegative rational number.

  Unless there is a risk of a `Module ℚ≥0 _` instance diamond, write `nnqsmul := _`. This will set
  `nnqsmul` to `(NNRat.cast · * ·)` thanks to unification in the default proof of `nnqsmul_def`.

  Do not use directly. Instead use the `•` notation. -/
  protected nnqsmul : ℚ≥0 → α → α
  /-- However `qsmul` is defined, it must be propositionally equal to multiplication by `Rat.cast`.

  Do not use this lemma directly. Use `NNRat.smul_def` instead. -/
  protected nnqsmul_def (q : ℚ≥0) (a : α) : nnqsmul q a = NNRat.cast q * a := by intros; rfl
  protected ratCast := Rat.castRec
  /-- However `Rat.cast q` is defined, it must be propositionally equal to `q.num / q.den`.

  Do not use this lemma directly. Use `Rat.cast_def` instead. -/
  protected ratCast_def (q : ℚ) : (Rat.cast q : α) = q.num / q.den := by intros; rfl
  /-- Scalar multiplication by a rational number.

  Unless there is a risk of a `Module ℚ _` instance diamond, write `qsmul := _`. This will set
  `qsmul` to `(Rat.cast · * ·)` thanks to unification in the default proof of `qsmul_def`.

  Do not use directly. Instead use the `•` notation. -/
  protected qsmul : ℚ → α → α
  /-- However `qsmul` is defined, it must be propositionally equal to multiplication by `Rat.cast`.

  Do not use this lemma directly. Use `Rat.cast_def` instead. -/
  protected qsmul_def (a : ℚ) (x : α) : qsmul a x = Rat.cast a * x := by intros; rfl
goal: DivisionRing.qsmul a x = ↑a * x

full_name: DivisionRing
code: /-- A `DivisionRing` is a `Ring` with multiplicative inverses for nonzero elements.

An instance of `DivisionRing K` includes maps `ratCast : ℚ → K` and `qsmul : ℚ → K → K`.
Those two fields are needed to implement the `DivisionRing K → Algebra ℚ K` instance since we need
to control the specific definitions for some special cases of `K` (in particular `K = ℚ` itself).
See also note [forgetful inheritance]. Similarly, there are maps `nnratCast ℚ≥0 → K` and
`nnqsmul : ℚ≥0 → K → K` to implement the `DivisionSemiring K → Algebra ℚ≥0 K` instance.

If the division ring has positive characteristic `p`, our division by zero convention forces
`ratCast (1 / p) = 1 / 0 = 0`. -/
class DivisionRing (α : Type*)
  extends Ring α, DivInvMonoid α, Nontrivial α, NNRatCast α, RatCast α where
  /-- For a nonzero `a`, `a⁻¹` is a right multiplicative inverse. -/
  protected mul_inv_cancel : ∀ (a : α), a ≠ 0 → a * a⁻¹ = 1
  /-- The inverse of `0` is `0` by convention. -/
  protected inv_zero : (0 : α)⁻¹ = 0
  protected nnratCast := NNRat.castRec
  /-- However `NNRat.cast` is defined, it must be equal to `a / b`.

  Do not use this lemma directly. Use `NNRat.cast_def` instead. -/
  protected nnratCast_def (q : ℚ≥0) : (NNRat.cast q : α) = q.num / q.den := by intros; rfl
  /-- Scalar multiplication by a nonnegative rational number.

  Unless there is a risk of a `Module ℚ≥0 _` instance diamond, write `nnqsmul := _`. This will set
  `nnqsmul` to `(NNRat.cast · * ·)` thanks to unification in the default proof of `nnqsmul_def`.

  Do not use directly. Instead use the `•` notation. -/
  protected nnqsmul : ℚ≥0 → α → α
  /-- However `qsmul` is defined, it must be propositionally equal to multiplication by `Rat.cast`.

  Do not use this lemma directly. Use `NNRat.smul_def` instead. -/
  protected nnqsmul_def (q : ℚ≥0) (a : α) : nnqsmul q a = NNRat.cast q * a := by intros; rfl
  protected ratCast := Rat.castRec
  /-- However `Rat.cast q` is defined, it must be propositionally equal to `q.num / q.den`.

  Do not use this lemma directly. Use `Rat.cast_def` instead. -/
  protected ratCast_def (q : ℚ) : (Rat.cast q : α) = q.num / q.den := by intros; rfl
  /-- Scalar multiplication by a rational number.

  Unless there is a risk of a `Module ℚ _` instance diamond, write `qsmul := _`. This will set
  `qsmul` to `(Rat.cast · * ·)` thanks to unification in the default proof of `qsmul_def`.

  Do not use directly. Instead use the `•` notation. -/
  protected qsmul : ℚ → α → α
  /-- However `qsmul` is defined, it must be propositionally equal to multiplication by `Rat.cast`.

  Do not use this lemma directly. Use `Rat.cast_def` instead. -/
  protected qsmul_def (a : ℚ) (x : α) : qsmul a x = Rat.cast a * x := by intros; rfl
goal: Type u_4

full_name: DivisionRing.ratCast_def
code: /-- A `DivisionRing` is a `Ring` with multiplicative inverses for nonzero elements.

An instance of `DivisionRing K` includes maps `ratCast : ℚ → K` and `qsmul : ℚ → K → K`.
Those two fields are needed to implement the `DivisionRing K → Algebra ℚ K` instance since we need
to control the specific definitions for some special cases of `K` (in particular `K = ℚ` itself).
See also note [forgetful inheritance]. Similarly, there are maps `nnratCast ℚ≥0 → K` and
`nnqsmul : ℚ≥0 → K → K` to implement the `DivisionSemiring K → Algebra ℚ≥0 K` instance.

If the division ring has positive characteristic `p`, our division by zero convention forces
`ratCast (1 / p) = 1 / 0 = 0`. -/
class DivisionRing (α : Type*)
  extends Ring α, DivInvMonoid α, Nontrivial α, NNRatCast α, RatCast α where
  /-- For a nonzero `a`, `a⁻¹` is a right multiplicative inverse. -/
  protected mul_inv_cancel : ∀ (a : α), a ≠ 0 → a * a⁻¹ = 1
  /-- The inverse of `0` is `0` by convention. -/
  protected inv_zero : (0 : α)⁻¹ = 0
  protected nnratCast := NNRat.castRec
  /-- However `NNRat.cast` is defined, it must be equal to `a / b`.

  Do not use this lemma directly. Use `NNRat.cast_def` instead. -/
  protected nnratCast_def (q : ℚ≥0) : (NNRat.cast q : α) = q.num / q.den := by intros; rfl
  /-- Scalar multiplication by a nonnegative rational number.

  Unless there is a risk of a `Module ℚ≥0 _` instance diamond, write `nnqsmul := _`. This will set
  `nnqsmul` to `(NNRat.cast · * ·)` thanks to unification in the default proof of `nnqsmul_def`.

  Do not use directly. Instead use the `•` notation. -/
  protected nnqsmul : ℚ≥0 → α → α
  /-- However `qsmul` is defined, it must be propositionally equal to multiplication by `Rat.cast`.

  Do not use this lemma directly. Use `NNRat.smul_def` instead. -/
  protected nnqsmul_def (q : ℚ≥0) (a : α) : nnqsmul q a = NNRat.cast q * a := by intros; rfl
  protected ratCast := Rat.castRec
  /-- However `Rat.cast q` is defined, it must be propositionally equal to `q.num / q.den`.

  Do not use this lemma directly. Use `Rat.cast_def` instead. -/
  protected ratCast_def (q : ℚ) : (Rat.cast q : α) = q.num / q.den := by intros; rfl
  /-- Scalar multiplication by a rational number.

  Unless there is a risk of a `Module ℚ _` instance diamond, write `qsmul := _`. This will set
  `qsmul` to `(Rat.cast · * ·)` thanks to unification in the default proof of `qsmul_def`.

  Do not use directly. Instead use the `•` notation. -/
  protected qsmul : ℚ → α → α
  /-- However `qsmul` is defined, it must be propositionally equal to multiplication by `Rat.cast`.

  Do not use this lemma directly. Use `Rat.cast_def` instead. -/
  protected qsmul_def (a : ℚ) (x : α) : qsmul a x = Rat.cast a * x := by intros; rfl
goal: ↑q = ↑q.num / ↑q.den

full_name: DivisionRing.nnqsmul_def
code: /-- A `DivisionRing` is a `Ring` with multiplicative inverses for nonzero elements.

An instance of `DivisionRing K` includes maps `ratCast : ℚ → K` and `qsmul : ℚ → K → K`.
Those two fields are needed to implement the `DivisionRing K → Algebra ℚ K` instance since we need
to control the specific definitions for some special cases of `K` (in particular `K = ℚ` itself).
See also note [forgetful inheritance]. Similarly, there are maps `nnratCast ℚ≥0 → K` and
`nnqsmul : ℚ≥0 → K → K` to implement the `DivisionSemiring K → Algebra ℚ≥0 K` instance.

If the division ring has positive characteristic `p`, our division by zero convention forces
`ratCast (1 / p) = 1 / 0 = 0`. -/
class DivisionRing (α : Type*)
  extends Ring α, DivInvMonoid α, Nontrivial α, NNRatCast α, RatCast α where
  /-- For a nonzero `a`, `a⁻¹` is a right multiplicative inverse. -/
  protected mul_inv_cancel : ∀ (a : α), a ≠ 0 → a * a⁻¹ = 1
  /-- The inverse of `0` is `0` by convention. -/
  protected inv_zero : (0 : α)⁻¹ = 0
  protected nnratCast := NNRat.castRec
  /-- However `NNRat.cast` is defined, it must be equal to `a / b`.

  Do not use this lemma directly. Use `NNRat.cast_def` instead. -/
  protected nnratCast_def (q : ℚ≥0) : (NNRat.cast q : α) = q.num / q.den := by intros; rfl
  /-- Scalar multiplication by a nonnegative rational number.

  Unless there is a risk of a `Module ℚ≥0 _` instance diamond, write `nnqsmul := _`. This will set
  `nnqsmul` to `(NNRat.cast · * ·)` thanks to unification in the default proof of `nnqsmul_def`.

  Do not use directly. Instead use the `•` notation. -/
  protected nnqsmul : ℚ≥0 → α → α
  /-- However `qsmul` is defined, it must be propositionally equal to multiplication by `Rat.cast`.

  Do not use this lemma directly. Use `NNRat.smul_def` instead. -/
  protected nnqsmul_def (q : ℚ≥0) (a : α) : nnqsmul q a = NNRat.cast q * a := by intros; rfl
  protected ratCast := Rat.castRec
  /-- However `Rat.cast q` is defined, it must be propositionally equal to `q.num / q.den`.

  Do not use this lemma directly. Use `Rat.cast_def` instead. -/
  protected ratCast_def (q : ℚ) : (Rat.cast q : α) = q.num / q.den := by intros; rfl
  /-- Scalar multiplication by a rational number.

  Unless there is a risk of a `Module ℚ _` instance diamond, write `qsmul := _`. This will set
  `qsmul` to `(Rat.cast · * ·)` thanks to unification in the default proof of `qsmul_def`.

  Do not use directly. Instead use the `•` notation. -/
  protected qsmul : ℚ → α → α
  /-- However `qsmul` is defined, it must be propositionally equal to multiplication by `Rat.cast`.

  Do not use this lemma directly. Use `Rat.cast_def` instead. -/
  protected qsmul_def (a : ℚ) (x : α) : qsmul a x = Rat.cast a * x := by intros; rfl
goal: DivisionRing.nnqsmul q a = ↑q * a

full_name: DivisionRing.qsmul
code: /-- A `DivisionRing` is a `Ring` with multiplicative inverses for nonzero elements.

An instance of `DivisionRing K` includes maps `ratCast : ℚ → K` and `qsmul : ℚ → K → K`.
Those two fields are needed to implement the `DivisionRing K → Algebra ℚ K` instance since we need
to control the specific definitions for some special cases of `K` (in particular `K = ℚ` itself).
See also note [forgetful inheritance]. Similarly, there are maps `nnratCast ℚ≥0 → K` and
`nnqsmul : ℚ≥0 → K → K` to implement the `DivisionSemiring K → Algebra ℚ≥0 K` instance.

If the division ring has positive characteristic `p`, our division by zero convention forces
`ratCast (1 / p) = 1 / 0 = 0`. -/
class DivisionRing (α : Type*)
  extends Ring α, DivInvMonoid α, Nontrivial α, NNRatCast α, RatCast α where
  /-- For a nonzero `a`, `a⁻¹` is a right multiplicative inverse. -/
  protected mul_inv_cancel : ∀ (a : α), a ≠ 0 → a * a⁻¹ = 1
  /-- The inverse of `0` is `0` by convention. -/
  protected inv_zero : (0 : α)⁻¹ = 0
  protected nnratCast := NNRat.castRec
  /-- However `NNRat.cast` is defined, it must be equal to `a / b`.

  Do not use this lemma directly. Use `NNRat.cast_def` instead. -/
  protected nnratCast_def (q : ℚ≥0) : (NNRat.cast q : α) = q.num / q.den := by intros; rfl
  /-- Scalar multiplication by a nonnegative rational number.

  Unless there is a risk of a `Module ℚ≥0 _` instance diamond, write `nnqsmul := _`. This will set
  `nnqsmul` to `(NNRat.cast · * ·)` thanks to unification in the default proof of `nnqsmul_def`.

  Do not use directly. Instead use the `•` notation. -/
  protected nnqsmul : ℚ≥0 → α → α
  /-- However `qsmul` is defined, it must be propositionally equal to multiplication by `Rat.cast`.

  Do not use this lemma directly. Use `NNRat.smul_def` instead. -/
  protected nnqsmul_def (q : ℚ≥0) (a : α) : nnqsmul q a = NNRat.cast q * a := by intros; rfl
  protected ratCast := Rat.castRec
  /-- However `Rat.cast q` is defined, it must be propositionally equal to `q.num / q.den`.

  Do not use this lemma directly. Use `Rat.cast_def` instead. -/
  protected ratCast_def (q : ℚ) : (Rat.cast q : α) = q.num / q.den := by intros; rfl
  /-- Scalar multiplication by a rational number.

  Unless there is a risk of a `Module ℚ _` instance diamond, write `qsmul := _`. This will set
  `qsmul` to `(Rat.cast · * ·)` thanks to unification in the default proof of `qsmul_def`.

  Do not use directly. Instead use the `•` notation. -/
  protected qsmul : ℚ → α → α
  /-- However `qsmul` is defined, it must be propositionally equal to multiplication by `Rat.cast`.

  Do not use this lemma directly. Use `Rat.cast_def` instead. -/
  protected qsmul_def (a : ℚ) (x : α) : qsmul a x = Rat.cast a * x := by intros; rfl
goal: ℚ → α → α

full_name: DivisionRing.nnratCast_def
code: /-- A `DivisionRing` is a `Ring` with multiplicative inverses for nonzero elements.

An instance of `DivisionRing K` includes maps `ratCast : ℚ → K` and `qsmul : ℚ → K → K`.
Those two fields are needed to implement the `DivisionRing K → Algebra ℚ K` instance since we need
to control the specific definitions for some special cases of `K` (in particular `K = ℚ` itself).
See also note [forgetful inheritance]. Similarly, there are maps `nnratCast ℚ≥0 → K` and
`nnqsmul : ℚ≥0 → K → K` to implement the `DivisionSemiring K → Algebra ℚ≥0 K` instance.

If the division ring has positive characteristic `p`, our division by zero convention forces
`ratCast (1 / p) = 1 / 0 = 0`. -/
class DivisionRing (α : Type*)
  extends Ring α, DivInvMonoid α, Nontrivial α, NNRatCast α, RatCast α where
  /-- For a nonzero `a`, `a⁻¹` is a right multiplicative inverse. -/
  protected mul_inv_cancel : ∀ (a : α), a ≠ 0 → a * a⁻¹ = 1
  /-- The inverse of `0` is `0` by convention. -/
  protected inv_zero : (0 : α)⁻¹ = 0
  protected nnratCast := NNRat.castRec
  /-- However `NNRat.cast` is defined, it must be equal to `a / b`.

  Do not use this lemma directly. Use `NNRat.cast_def` instead. -/
  protected nnratCast_def (q : ℚ≥0) : (NNRat.cast q : α) = q.num / q.den := by intros; rfl
  /-- Scalar multiplication by a nonnegative rational number.

  Unless there is a risk of a `Module ℚ≥0 _` instance diamond, write `nnqsmul := _`. This will set
  `nnqsmul` to `(NNRat.cast · * ·)` thanks to unification in the default proof of `nnqsmul_def`.

  Do not use directly. Instead use the `•` notation. -/
  protected nnqsmul : ℚ≥0 → α → α
  /-- However `qsmul` is defined, it must be propositionally equal to multiplication by `Rat.cast`.

  Do not use this lemma directly. Use `NNRat.smul_def` instead. -/
  protected nnqsmul_def (q : ℚ≥0) (a : α) : nnqsmul q a = NNRat.cast q * a := by intros; rfl
  protected ratCast := Rat.castRec
  /-- However `Rat.cast q` is defined, it must be propositionally equal to `q.num / q.den`.

  Do not use this lemma directly. Use `Rat.cast_def` instead. -/
  protected ratCast_def (q : ℚ) : (Rat.cast q : α) = q.num / q.den := by intros; rfl
  /-- Scalar multiplication by a rational number.

  Unless there is a risk of a `Module ℚ _` instance diamond, write `qsmul := _`. This will set
  `qsmul` to `(Rat.cast · * ·)` thanks to unification in the default proof of `qsmul_def`.

  Do not use directly. Instead use the `•` notation. -/
  protected qsmul : ℚ → α → α
  /-- However `qsmul` is defined, it must be propositionally equal to multiplication by `Rat.cast`.

  Do not use this lemma directly. Use `Rat.cast_def` instead. -/
  protected qsmul_def (a : ℚ) (x : α) : qsmul a x = Rat.cast a * x := by intros; rfl
goal: ↑q = ↑q.num / ↑q.den

full_name: DivisionRing.mul_inv_cancel
code: /-- A `DivisionRing` is a `Ring` with multiplicative inverses for nonzero elements.

An instance of `DivisionRing K` includes maps `ratCast : ℚ → K` and `qsmul : ℚ → K → K`.
Those two fields are needed to implement the `DivisionRing K → Algebra ℚ K` instance since we need
to control the specific definitions for some special cases of `K` (in particular `K = ℚ` itself).
See also note [forgetful inheritance]. Similarly, there are maps `nnratCast ℚ≥0 → K` and
`nnqsmul : ℚ≥0 → K → K` to implement the `DivisionSemiring K → Algebra ℚ≥0 K` instance.

If the division ring has positive characteristic `p`, our division by zero convention forces
`ratCast (1 / p) = 1 / 0 = 0`. -/
class DivisionRing (α : Type*)
  extends Ring α, DivInvMonoid α, Nontrivial α, NNRatCast α, RatCast α where
  /-- For a nonzero `a`, `a⁻¹` is a right multiplicative inverse. -/
  protected mul_inv_cancel : ∀ (a : α), a ≠ 0 → a * a⁻¹ = 1
  /-- The inverse of `0` is `0` by convention. -/
  protected inv_zero : (0 : α)⁻¹ = 0
  protected nnratCast := NNRat.castRec
  /-- However `NNRat.cast` is defined, it must be equal to `a / b`.

  Do not use this lemma directly. Use `NNRat.cast_def` instead. -/
  protected nnratCast_def (q : ℚ≥0) : (NNRat.cast q : α) = q.num / q.den := by intros; rfl
  /-- Scalar multiplication by a nonnegative rational number.

  Unless there is a risk of a `Module ℚ≥0 _` instance diamond, write `nnqsmul := _`. This will set
  `nnqsmul` to `(NNRat.cast · * ·)` thanks to unification in the default proof of `nnqsmul_def`.

  Do not use directly. Instead use the `•` notation. -/
  protected nnqsmul : ℚ≥0 → α → α
  /-- However `qsmul` is defined, it must be propositionally equal to multiplication by `Rat.cast`.

  Do not use this lemma directly. Use `NNRat.smul_def` instead. -/
  protected nnqsmul_def (q : ℚ≥0) (a : α) : nnqsmul q a = NNRat.cast q * a := by intros; rfl
  protected ratCast := Rat.castRec
  /-- However `Rat.cast q` is defined, it must be propositionally equal to `q.num / q.den`.

  Do not use this lemma directly. Use `Rat.cast_def` instead. -/
  protected ratCast_def (q : ℚ) : (Rat.cast q : α) = q.num / q.den := by intros; rfl
  /-- Scalar multiplication by a rational number.

  Unless there is a risk of a `Module ℚ _` instance diamond, write `qsmul := _`. This will set
  `qsmul` to `(Rat.cast · * ·)` thanks to unification in the default proof of `qsmul_def`.

  Do not use directly. Instead use the `•` notation. -/
  protected qsmul : ℚ → α → α
  /-- However `qsmul` is defined, it must be propositionally equal to multiplication by `Rat.cast`.

  Do not use this lemma directly. Use `Rat.cast_def` instead. -/
  protected qsmul_def (a : ℚ) (x : α) : qsmul a x = Rat.cast a * x := by intros; rfl
goal: a ≠ 0 → a * a⁻¹ = 1

full_name: DivisionRing.toDivisionSemiring
code: instance (priority := 100) DivisionRing.toDivisionSemiring [DivisionRing α] : DivisionSemiring α 
goal: DivisionSemiring α

full_name: Semifield
code: /-- A `Semifield` is a `CommSemiring` with multiplicative inverses for nonzero elements.

An instance of `Semifield K` includes maps `nnratCast : ℚ≥0 → K` and `nnqsmul : ℚ≥0 → K → K`.
Those two fields are needed to implement the `DivisionSemiring K → Algebra ℚ≥0 K` instance since we
need to control the specific definitions for some special cases of `K` (in particular `K = ℚ≥0`
itself). See also note [forgetful inheritance].

If the semifield has positive characteristic `p`, our division by zero convention forces
`nnratCast (1 / p) = 1 / 0 = 0`. -/
class Semifield (α : Type*) extends CommSemiring α, DivisionSemiring α, CommGroupWithZero α
goal: Type u_4

full_name: Field
code: /-- A `Field` is a `CommRing` with multiplicative inverses for nonzero elements.

An instance of `Field K` includes maps `ratCast : ℚ → K` and `qsmul : ℚ → K → K`.
Those two fields are needed to implement the `DivisionRing K → Algebra ℚ K` instance since we need
to control the specific definitions for some special cases of `K` (in particular `K = ℚ` itself).
See also note [forgetful inheritance].

If the field has positive characteristic `p`, our division by zero convention forces
`ratCast (1 / p) = 1 / 0 = 0`. -/
class Field (K : Type u) extends CommRing K, DivisionRing K
goal: Type u

full_name: Field.toSemifield
code: instance (priority := 100) Field.toSemifield [Field α] : Semifield α 
goal: Semifield α

full_name: NNRat.smulDivisionSemiring
code: instance (priority := 100) smulDivisionSemiring : SMul ℚ≥0 α 
goal: SMul ℚ≥0 α

full_name: NNRat.cast_def
code: lemma cast_def (q : ℚ≥0) : (q : α) = q.num / q.den 
goal: ↑q = ↑q.num / ↑q.den

full_name: NNRat.smul_def
code: lemma smul_def (q : ℚ≥0) (a : α) : q • a = q * a 
goal: q • a = ↑q * a

full_name: NNRat.smul_one_eq_cast
code: @[simp] lemma smul_one_eq_cast (q : ℚ≥0) : q • (1 : α) = q 
goal: q • 1 = ↑q

full_name: Rat.cast_def
code: lemma cast_def (q : ℚ) : (q : K) = q.num / q.den 
goal: ↑q = ↑q.num / ↑q.den

full_name: Rat.cast_mk'
code: lemma cast_mk' (a b h1 h2) : ((⟨a, b, h1, h2⟩ : ℚ) : K) = a / b 
goal: ↑{ num := a, den := b, den_nz := h1, reduced := h2 } = ↑a / ↑b

full_name: Rat.smulDivisionRing
code: instance (priority := 100) smulDivisionRing : SMul ℚ K 
goal: SMul ℚ K

full_name: Rat.smul_def
code: theorem smul_def (a : ℚ) (x : K) : a • x = ↑a * x 
goal: a • x = ↑a * x

full_name: Rat.smul_one_eq_cast
code: @[simp]
theorem smul_one_eq_cast (A : Type*) [DivisionRing A] (m : ℚ) : m • (1 : A) = ↑m 
goal: m • 1 = ↑m

full_name: Rat.ofScientific_eq_ofScientific
code: /-- `OfScientific.ofScientific` is the simp-normal form. -/
@[simp]
theorem Rat.ofScientific_eq_ofScientific (m : ℕ) (s : Bool) (e : ℕ) :
    Rat.ofScientific (OfNat.ofNat m) s (OfNat.ofNat e) = OfScientific.ofScientific m s e 
goal: Rat.ofScientific (OfNat.ofNat m) s (OfNat.ofNat e) = OfScientific.ofScientific m s e