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feat: port Algebra.Order.Nonneg.Field (#2200)
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/- | ||
Copyright (c) 2021 Floris van Doorn. All rights reserved. | ||
Released under Apache 2.0 license as described in the file LICENSE. | ||
Authors: Floris van Doorn | ||
! This file was ported from Lean 3 source module algebra.order.nonneg.field | ||
! leanprover-community/mathlib commit dc6c365e751e34d100e80fe6e314c3c3e0fd2988 | ||
! Please do not edit these lines, except to modify the commit id | ||
! if you have ported upstream changes. | ||
-/ | ||
import Mathlib.Algebra.Order.Archimedean | ||
import Mathlib.Algebra.Order.Nonneg.Ring | ||
import Mathlib.Algebra.Order.Field.InjSurj | ||
import Mathlib.Algebra.Order.Field.Canonical.Defs | ||
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/-! | ||
# Semifield structure on the type of nonnegative elements | ||
This file defines instances and prove some properties about the nonnegative elements | ||
`{x : α // 0 ≤ x}` of an arbitrary type `α`. | ||
This is used to derive algebraic structures on `ℝ≥0` and `ℚ≥0` automatically. | ||
## Main declarations | ||
* `{x : α // 0 ≤ x}` is a `CanonicallyLinearOrderedSemifield` if `α` is a `LinearOrderedField`. | ||
-/ | ||
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open Set | ||
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variable {α : Type _} | ||
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namespace Nonneg | ||
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section LinearOrderedSemifield | ||
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variable [LinearOrderedSemifield α] {x y : α} | ||
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instance inv : Inv { x : α // 0 ≤ x } := | ||
⟨fun x => ⟨x⁻¹, inv_nonneg.2 x.2⟩⟩ | ||
#align nonneg.has_inv Nonneg.inv | ||
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@[simp, norm_cast] | ||
protected theorem coe_inv (a : { x : α // 0 ≤ x }) : ((a⁻¹ : { x : α // 0 ≤ x }) : α) = (a : α)⁻¹ := | ||
rfl | ||
#align nonneg.coe_inv Nonneg.coe_inv | ||
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@[simp] | ||
theorem inv_mk (hx : 0 ≤ x) : (⟨x, hx⟩ : { x : α // 0 ≤ x })⁻¹ = ⟨x⁻¹, inv_nonneg.2 hx⟩ := | ||
rfl | ||
#align nonneg.inv_mk Nonneg.inv_mk | ||
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instance hasDiv : Div { x : α // 0 ≤ x } := | ||
⟨fun x y => ⟨x / y, div_nonneg x.2 y.2⟩⟩ | ||
#align nonneg.has_div Nonneg.hasDiv | ||
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@[simp, norm_cast] | ||
protected theorem coe_div (a b : { x : α // 0 ≤ x }) : ((a / b : { x : α // 0 ≤ x }) : α) = a / b := | ||
rfl | ||
#align nonneg.coe_div Nonneg.coe_div | ||
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@[simp] | ||
theorem mk_div_mk (hx : 0 ≤ x) (hy : 0 ≤ y) : | ||
(⟨x, hx⟩ : { x : α // 0 ≤ x }) / ⟨y, hy⟩ = ⟨x / y, div_nonneg hx hy⟩ := | ||
rfl | ||
#align nonneg.mk_div_mk Nonneg.mk_div_mk | ||
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instance hasZpow : Pow { x : α // 0 ≤ x } ℤ := | ||
⟨fun a n => ⟨(a : α) ^ n, zpow_nonneg a.2 _⟩⟩ | ||
#align nonneg.has_zpow Nonneg.hasZpow | ||
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@[simp, norm_cast] | ||
protected theorem coe_zpow (a : { x : α // 0 ≤ x }) (n : ℤ) : | ||
((a ^ n : { x : α // 0 ≤ x }) : α) = (a : α) ^ n := | ||
rfl | ||
#align nonneg.coe_zpow Nonneg.coe_zpow | ||
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@[simp] | ||
theorem mk_zpow (hx : 0 ≤ x) (n : ℤ) : | ||
(⟨x, hx⟩ : { x : α // 0 ≤ x }) ^ n = ⟨x ^ n, zpow_nonneg hx n⟩ := | ||
rfl | ||
#align nonneg.mk_zpow Nonneg.mk_zpow | ||
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instance linearOrderedSemifield : LinearOrderedSemifield { x : α // 0 ≤ x } := | ||
Subtype.coe_injective.linearOrderedSemifield _ Nonneg.coe_zero Nonneg.coe_one Nonneg.coe_add | ||
Nonneg.coe_mul Nonneg.coe_inv Nonneg.coe_div (fun _ _ => rfl) Nonneg.coe_pow Nonneg.coe_zpow | ||
Nonneg.coe_nat_cast (fun _ _ => rfl) fun _ _ => rfl | ||
#align nonneg.linear_ordered_semifield Nonneg.linearOrderedSemifield | ||
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end LinearOrderedSemifield | ||
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instance canonicallyLinearOrderedSemifield [LinearOrderedField α] : | ||
CanonicallyLinearOrderedSemifield { x : α // 0 ≤ x } := | ||
{ Nonneg.linearOrderedSemifield, Nonneg.canonicallyOrderedCommSemiring with } | ||
#align nonneg.canonically_linear_ordered_semifield Nonneg.canonicallyLinearOrderedSemifield | ||
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instance linearOrderedCommGroupWithZero [LinearOrderedField α] : | ||
LinearOrderedCommGroupWithZero { x : α // 0 ≤ x } := | ||
inferInstance | ||
#align nonneg.linear_ordered_comm_group_with_zero Nonneg.linearOrderedCommGroupWithZero | ||
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/-! ### Floor -/ | ||
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instance archimedean [OrderedAddCommMonoid α] [Archimedean α] : Archimedean { x : α // 0 ≤ x } := | ||
⟨fun x y hy => | ||
let ⟨n, hr⟩ := Archimedean.arch (x : α) (hy : (0 : α) < y) | ||
⟨n, show (x : α) ≤ (n • y : { x : α // 0 ≤ x }) by simp [*, -nsmul_eq_mul, nsmul_coe]⟩⟩ | ||
#align nonneg.archimedean Nonneg.archimedean | ||
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instance floorSemiring [OrderedSemiring α] [FloorSemiring α] : | ||
FloorSemiring { r : α // 0 ≤ r } where | ||
floor a := ⌊(a : α)⌋₊ | ||
ceil a := ⌈(a : α)⌉₊ | ||
floor_of_neg ha := FloorSemiring.floor_of_neg ha | ||
gc_floor ha := FloorSemiring.gc_floor (Subtype.coe_le_coe.2 ha) | ||
gc_ceil a n := FloorSemiring.gc_ceil (a : α) n | ||
#align nonneg.floor_semiring Nonneg.floorSemiring | ||
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@[norm_cast] | ||
theorem nat_floor_coe [OrderedSemiring α] [FloorSemiring α] (a : { r : α // 0 ≤ r }) : | ||
⌊(a : α)⌋₊ = ⌊a⌋₊ := | ||
rfl | ||
#align nonneg.nat_floor_coe Nonneg.nat_floor_coe | ||
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@[norm_cast] | ||
theorem nat_ceil_coe [OrderedSemiring α] [FloorSemiring α] (a : { r : α // 0 ≤ r }) : | ||
⌈(a : α)⌉₊ = ⌈a⌉₊ := | ||
rfl | ||
#align nonneg.nat_ceil_coe Nonneg.nat_ceil_coe | ||
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end Nonneg |