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agdaproofs/Fields/CauchyCompletion/Approximation.agda
Patrick Stevens 55995ea801 Minor perf improvements? (#60)
2019-11-02 08:57:15 +00:00

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{-# OPTIONS --safe --warning=error --without-K --guardedness #-}
open import Agda.Primitive using (Level; lzero; lsuc; _⊔_)
open import Orders
open import Setoids.Setoids
open import Rings.Definition
open import Rings.Lemmas
open import Rings.Orders.Definition
open import Groups.Definition
open import Groups.Groups
open import Fields.Fields
open import Sets.EquivalenceRelations
open import Sequences
open import Setoids.Orders
open import Functions
open import LogicalFormulae
open import Numbers.Naturals.Naturals
open import Numbers.Naturals.Order
open import Semirings.Definition
module Fields.CauchyCompletion.Approximation {m n o : _} {A : Set m} {S : Setoid {m} {n} A} {_+_ : A → A → A} {_*_ : A → A → A} {_<_ : Rel {m} {o} A} {pOrder : SetoidPartialOrder S _<_} {tOrder : SetoidTotalOrder {_<_ = _<_} pOrder} {R : Ring S _+_ _*_} (order : OrderedRing R tOrder) (F : Field R) (charNot2 : Setoid._∼_ S ((Ring.1R R) + (Ring.1R R)) (Ring.0R R) → False) where
open Setoid S
open SetoidTotalOrder tOrder
open SetoidPartialOrder pOrder
open Equivalence eq
open OrderedRing order
open Ring R
open Group additiveGroup
open Field F
open import Fields.Lemmas F
open import Fields.Orders.Lemmas {F = F} record { oRing = order }
open import Rings.Orders.Lemmas(order)
open import Fields.CauchyCompletion.Definition order F
open import Fields.CauchyCompletion.Addition order F charNot2
open import Fields.CauchyCompletion.Setoid order F charNot2
open import Fields.CauchyCompletion.Comparison order F charNot2
abstract
chain : {a b : A} (c : CauchyCompletion) → (a r<C c) → (c <Cr b) → a < b
chain {a} {b} c (betweenAC , (0<betweenAC ,, (Nac , prAC))) (betweenCB , (0<betweenCB ,, (Nb , prBC))) = SetoidPartialOrder.transitive pOrder (SetoidPartialOrder.transitive pOrder (<WellDefined identLeft (Equivalence.reflexive eq) (orderRespectsAddition 0<betweenAC a)) (<WellDefined groupIsAbelian (Equivalence.reflexive eq) (SetoidPartialOrder.transitive pOrder (prAC (succ Nac +N Nb) (le Nb (applyEquality succ (Semiring.commutative ℕSemiring Nb Nac)))) (<WellDefined identLeft (Equivalence.reflexive eq) (orderRespectsAddition 0<betweenCB (index (Sequence.tail (CauchyCompletion.elts c)) (Nac +N Nb))))))) (prBC (succ Nac +N Nb) (le Nac refl))
approxLemma : (a : CauchyCompletion) (e e/2 : A) → (0G < e) → (e/2 + e/2 ∼ e) → (m N : ℕ) → abs ((index (CauchyCompletion.elts a) m) + inverse (index (CauchyCompletion.elts a) N)) < e/2 → (e/2 + index (CauchyCompletion.elts a) m) < (index (CauchyCompletion.elts a) N + e)
approxLemma a e e/2 0<e prE/2 m N ans with SetoidTotalOrder.totality tOrder 0R ((index (CauchyCompletion.elts a) m) + inverse (index (CauchyCompletion.elts a) N))
approxLemma a e e/2 0<e prE/2 m N ans | inl (inl x) with <WellDefined (Equivalence.transitive eq (Equivalence.transitive eq (Equivalence.symmetric eq +Associative) (+WellDefined (Equivalence.reflexive eq) (invLeft))) identRight) groupIsAbelian (orderRespectsAddition ans (index (CauchyCompletion.elts a) N))
... | bl = <WellDefined groupIsAbelian (Equivalence.transitive eq (Equivalence.symmetric eq +Associative) (+WellDefined (Equivalence.reflexive eq) prE/2)) (orderRespectsAddition bl e/2)
approxLemma a e e/2 0<e prE/2 m N ans | inl (inr x) with <WellDefined (Equivalence.transitive eq (Equivalence.transitive eq (Equivalence.symmetric eq +Associative) (+WellDefined (Equivalence.reflexive eq) (invLeft))) identRight) (identLeft) (orderRespectsAddition x (index (CauchyCompletion.elts a) N))
... | bl = <WellDefined groupIsAbelian (Equivalence.reflexive eq) (ringAddInequalities bl (halfLess e/2 e 0<e prE/2))
approxLemma a e e/2 0<e prE/2 m N ans | inr x with transferToRight additiveGroup (Equivalence.symmetric eq x)
... | bl = <WellDefined (+WellDefined (Equivalence.reflexive eq) (Equivalence.symmetric eq bl)) groupIsAbelian (orderRespectsAddition (halfLess e/2 e 0<e prE/2) (index (CauchyCompletion.elts a) N))
approximateAboveCrude : (a : CauchyCompletion) → Sg A (λ b → (a <Cr b))
approximateAboveCrude a with CauchyCompletion.converges a 1R (0<1 (charNot2ImpliesNontrivial charNot2))
... | N , conv = ((((index (CauchyCompletion.elts a) (succ N)) + 1R) + 1R) + 1R) , (1R , (0<1 (charNot2ImpliesNontrivial charNot2) ,, (N , ans)))
where
ans : (m : ℕ) → (N <N m) → (1R + index (CauchyCompletion.elts a) m) < (((index (CauchyCompletion.elts a) (succ N) + 1R) + 1R) + 1R)
ans m N<m with conv {m} {succ N} N<m (le 0 refl)
... | bl with totality 0G (index (CauchyCompletion.elts a) m + inverse (index (CauchyCompletion.elts a) (succ N)))
ans m N<m | bl | inl (inl 0<am-aN) with <WellDefined (Equivalence.transitive eq (Equivalence.transitive eq (Equivalence.symmetric eq +Associative) (+WellDefined (Equivalence.reflexive eq) (invLeft))) identRight) (Equivalence.reflexive eq) (orderRespectsAddition bl (index (CauchyCompletion.elts a) (succ N)))
... | am<1+an = <WellDefined (Equivalence.transitive eq (+WellDefined (Equivalence.reflexive eq) identLeft) groupIsAbelian) (Equivalence.transitive eq (+WellDefined groupIsAbelian (Equivalence.reflexive eq)) +Associative) (ringAddInequalities am<1+an (orderRespectsAddition (0<1 (charNot2ImpliesNontrivial charNot2)) 1R))
ans m N<m | bl | inl (inr am-aN<0) with <WellDefined (Equivalence.transitive eq (Equivalence.transitive eq (Equivalence.symmetric eq +Associative) (+WellDefined (Equivalence.reflexive eq) invLeft)) identRight) identLeft (orderRespectsAddition am-aN<0 (index (CauchyCompletion.elts a) (succ N)))
... | am<aN = <WellDefined groupIsAbelian (Equivalence.reflexive eq) (orderRespectsAddition (SetoidPartialOrder.transitive pOrder am<aN (<WellDefined (Equivalence.reflexive eq) (+Associative) (<WellDefined identLeft groupIsAbelian (orderRespectsAddition (<WellDefined identLeft (Equivalence.reflexive eq) (ringAddInequalities (0<1 (charNot2ImpliesNontrivial charNot2)) (0<1 (charNot2ImpliesNontrivial charNot2)))) (index (CauchyCompletion.elts a) (succ N)))))) 1R)
ans m N<m | bl | inr 0=am-aN = <WellDefined (Equivalence.transitive eq (+WellDefined identLeft (Equivalence.reflexive eq)) identLeft) (Equivalence.transitive eq groupIsAbelian (Equivalence.transitive eq (+WellDefined (Equivalence.transitive eq groupIsAbelian (+WellDefined (transferToRight additiveGroup (Equivalence.symmetric eq 0=am-aN)) (Equivalence.reflexive eq))) (Equivalence.reflexive eq)) +Associative)) (orderRespectsAddition (ringAddInequalities (0<1 (charNot2ImpliesNontrivial charNot2)) (0<1 (charNot2ImpliesNontrivial charNot2))) (1R + (index (CauchyCompletion.elts a) m)))
rationalApproximatelyAbove : (a : CauchyCompletion) → (e : A) → (0G < e) → A
rationalApproximatelyAbove a e 0<e with halve charNot2 e
... | e/2 , prE/2 with halvePositive e/2 (<WellDefined (Equivalence.reflexive eq) (Equivalence.symmetric eq prE/2) 0<e)
... | 0<e/2 with halve charNot2 e/2
... | e/4 , prE/4 with halvePositive e/4 (<WellDefined (Equivalence.reflexive eq) (Equivalence.symmetric eq prE/4) 0<e/2)
... | 0<e/4 with CauchyCompletion.converges a e/4 0<e/4
... | N , cauchyBeyondN = index (CauchyCompletion.elts a) (succ N) + e/2
rationalApproximatelyAboveIsAbove : (a : CauchyCompletion) (e : A) → (0<e : 0G < e) → a <Cr (rationalApproximatelyAbove a e 0<e)
rationalApproximatelyAboveIsAbove a e 0<e with halve charNot2 e
... | e/2 , prE/2 with halvePositive e/2 (<WellDefined (Equivalence.reflexive eq) (Equivalence.symmetric eq prE/2) 0<e)
... | 0<e/2 with halve charNot2 e/2
... | e/4 , prE/4 with halvePositive e/4 (<WellDefined (Equivalence.reflexive eq) (Equivalence.symmetric eq prE/4) 0<e/2)
... | 0<e/4 with CauchyCompletion.converges a e/4 0<e/4
... | N , cauchyBeyondN with halve charNot2 e/4
... | e/8 , prE/8 with halvePositive e/8 (<WellDefined (Equivalence.reflexive eq) (Equivalence.symmetric eq prE/8) 0<e/4)
... | 0<e/8 with CauchyCompletion.converges a e/8 0<e/8
... | N2 , cauchyBeyondN2 = e/8 , (0<e/8 ,, ((N +N N2) , ans2))
where
ans2 : (m : ℕ) → N +N N2 <N m → (e/8 + index (CauchyCompletion.elts a) m) < (index (CauchyCompletion.elts a) (succ N) + e/2)
ans2 m <m with cauchyBeyondN {m} {succ N} (inequalityShrinkLeft <m) (le 0 refl)
... | absam-aN<e/4 with totality 0R ((index (CauchyCompletion.elts a) m) + inverse (index (CauchyCompletion.elts a) (succ N)))
ans2 m <m | am-aN<e/4 | inl (inl 0<am-aN) = SetoidPartialOrder.transitive pOrder (<WellDefined groupIsAbelian (Equivalence.transitive eq groupIsAbelian +Associative) (orderRespectsAddition (<WellDefined (Equivalence.transitive eq (Equivalence.transitive eq (Equivalence.symmetric eq +Associative) (+WellDefined (Equivalence.reflexive eq) invLeft)) identRight) (Equivalence.reflexive eq) (orderRespectsAddition am-aN<e/4 (index (CauchyCompletion.elts a) (succ N)))) e/8)) (<WellDefined (Equivalence.reflexive eq) groupIsAbelian (orderRespectsAddition (<WellDefined (Equivalence.reflexive eq) prE/4 (orderRespectsAddition (halfLess e/8 e/4 0<e/4 prE/8) e/4)) (index (CauchyCompletion.elts a) (succ N))))
ans2 m <m | -[am-aN]<e/4 | inl (inr am-aN<0) with <WellDefined (Equivalence.transitive eq +Associative (Equivalence.transitive eq (+WellDefined invLeft (Equivalence.reflexive eq)) identLeft)) (Equivalence.reflexive eq) (orderRespectsAddition (<WellDefined (Equivalence.reflexive eq) (invTwice additiveGroup _) (ringSwapNegatives' -[am-aN]<e/4)) (e/4 + e/8))
... | e/8<am-aN+e/4+e/8 = SetoidPartialOrder.transitive pOrder (orderRespectsAddition e/8<am-aN+e/4+e/8 (index (CauchyCompletion.elts a) m)) (<WellDefined (Equivalence.reflexive eq) groupIsAbelian (ringAddInequalities (<WellDefined (Equivalence.reflexive eq) identLeft (ringAddInequalities am-aN<0 (<WellDefined groupIsAbelian prE/4 (orderRespectsAddition (halfLess e/8 e/4 0<e/4 prE/8) e/4)))) am<aN))
where
am<aN : (index (CauchyCompletion.elts a) m) < (index (CauchyCompletion.elts a) (succ N))
am<aN = <WellDefined (Equivalence.transitive eq (Equivalence.transitive eq (Equivalence.symmetric eq +Associative) (+WellDefined (Equivalence.reflexive eq) groupIsAbelian)) (Equivalence.transitive eq (+WellDefined (Equivalence.reflexive eq) invRight) identRight)) identLeft (orderRespectsAddition am-aN<0 (index (CauchyCompletion.elts a) (succ N)))
ans2 m <m | absam-aN<e/4 | inr 0=am-aN = <WellDefined (Equivalence.reflexive eq) (Equivalence.transitive eq groupIsAbelian (+WellDefined (transferToRight additiveGroup (Equivalence.symmetric eq 0=am-aN)) (Equivalence.reflexive eq))) (orderRespectsAddition {b = e/2} (SetoidPartialOrder.transitive pOrder (halfLess e/8 e/4 0<e/4 prE/8) (halfLess e/4 e/2 0<e/2 prE/4)) (index (CauchyCompletion.elts a) m))
rationalApproximatelyAboveIsNear : (a : CauchyCompletion) (e : A) → (0<e : 0G < e) → (injection (rationalApproximatelyAbove a e 0<e) +C (-C a)) <C (injection e)
rationalApproximatelyAboveIsNear a e 0<e with halve charNot2 e
... | e/2 , prE/2 with halvePositive e/2 (<WellDefined (Equivalence.reflexive eq) (Equivalence.symmetric eq prE/2) 0<e)
... | 0<e/2 with halve charNot2 e/2
... | e/4 , prE/4 with halvePositive e/4 (<WellDefined (Equivalence.reflexive eq) (Equivalence.symmetric eq prE/4) 0<e/2)
... | 0<e/4 with CauchyCompletion.converges a e/4 0<e/4
... | N , cauchyBeyondN with halve charNot2 e/4
... | e/8 , prE/8 with halvePositive e/8 (<WellDefined (Equivalence.reflexive eq) (Equivalence.symmetric eq prE/8) 0<e/4)
... | 0<e/8 with CauchyCompletion.converges a e/8 0<e/8
... | N8 , cauchyBeyondN8 with halve charNot2 e/8
... | e/16 , prE/16 with halvePositive e/16 (<WellDefined (Equivalence.reflexive eq) (Equivalence.symmetric eq prE/16) 0<e/8)
... | 0<e/16 = ((e/2 + e/4) + e/8) , ((e/8 , (0<e/8 ,, ((N +N N8) , ans))) ,, (e/16 , (0<e/16 ,, (0 , t'))))
where
t' : (m : ℕ) → (0 <N m) → (((e/2 + e/4) + e/8) + e/16) < index (constSequence e) m
t' m 0<m rewrite indexAndConst e m = <WellDefined (Equivalence.reflexive eq) prE/2 (<WellDefined (Equivalence.reflexive eq) (+WellDefined (Equivalence.reflexive eq) prE/4) (<WellDefined +Associative (Equivalence.symmetric eq +Associative) (<WellDefined groupIsAbelian groupIsAbelian (orderRespectsAddition (<WellDefined (Equivalence.reflexive eq) prE/8 (<WellDefined groupIsAbelian groupIsAbelian (orderRespectsAddition (halfLess e/16 e/8 0<e/8 prE/16) e/8))) (e/2 + e/4)))))
ans : (m : ℕ) → (N +N N8) <N m → (e/8 + index (apply _+_ (constSequence (index (CauchyCompletion.elts a) (succ N) + e/2)) (map inverse (CauchyCompletion.elts a))) m) < ((e/2 + e/4) + e/8)
ans m N<m rewrite indexAndApply (constSequence (index (CauchyCompletion.elts a) (succ N) + e/2)) (map inverse (CauchyCompletion.elts a)) _+_ {m} | indexAndConst (index (CauchyCompletion.elts a) (succ N) + e/2) m | equalityCommutative (mapAndIndex (CauchyCompletion.elts a) inverse m) = <WellDefined groupIsAbelian (+WellDefined groupIsAbelian (Equivalence.reflexive eq)) (orderRespectsAddition (<WellDefined (Equivalence.transitive eq groupIsAbelian (Equivalence.reflexive eq)) (Equivalence.reflexive eq) q) e/8)
where
am = index (CauchyCompletion.elts a) m
aN = index (CauchyCompletion.elts a) (succ N)
t : abs (am + inverse aN) < e/4
t = cauchyBeyondN {m} {succ N} (inequalityShrinkLeft N<m) (le 0 refl)
r : ((inverse am) + aN) < e/4
r with t
... | f with totality 0G (am + inverse aN)
r | am-aN<e/4 | inl (inl 0<am-aN) = SetoidPartialOrder.transitive pOrder (<WellDefined (Equivalence.transitive eq (invContravariant additiveGroup) (Equivalence.transitive eq groupIsAbelian (+WellDefined (Equivalence.reflexive eq) (invTwice additiveGroup _)))) (Equivalence.reflexive eq) (lemm2' _ 0<am-aN)) 0<e/4
r | f | inl (inr x) = <WellDefined (Equivalence.transitive eq (invContravariant additiveGroup) (Equivalence.transitive eq groupIsAbelian (+WellDefined (Equivalence.reflexive eq) (invTwice additiveGroup _)))) (Equivalence.reflexive eq) f
r | am-aN<e/4 | inr 0=am-aN = <WellDefined (Equivalence.transitive eq (Equivalence.symmetric eq 0=am-aN) (Equivalence.transitive eq (Equivalence.transitive eq (Equivalence.transitive eq (Equivalence.transitive eq (Equivalence.symmetric eq (invIdentity additiveGroup)) (inverseWellDefined additiveGroup 0=am-aN)) (inverseWellDefined additiveGroup groupIsAbelian)) (invContravariant additiveGroup)) (+WellDefined (Equivalence.reflexive eq) (invTwice additiveGroup _)))) (Equivalence.reflexive eq) am-aN<e/4
q : ((inverse (index (CauchyCompletion.elts a) m)) + (index (CauchyCompletion.elts a) (succ N) + e/2)) < (e/4 + e/2)
q = <WellDefined (Equivalence.symmetric eq +Associative) (Equivalence.reflexive eq) (orderRespectsAddition r e/2)
approximateAbove : (a : CauchyCompletion) → (ε : A) → (0G < ε) → Sg A (λ b → (a <Cr b) && (injection b +C (-C a)) <C (injection ε))
approximateAbove a e 0<e = rationalApproximatelyAbove a e 0<e , (rationalApproximatelyAboveIsAbove a e 0<e ,, rationalApproximatelyAboveIsNear a e 0<e)
approximateBelow : (a : CauchyCompletion) → (ε : A) → (0G < ε) → Sg A (λ b → (b r<C a) && (a +C (-C injection b)) <C (injection ε))
approximateBelow a e 0<e with approximateAbove (-C a) e 0<e
... | x , ((deltaXAnd-A , (0<deltaXA ,, (NdeltaXA , prDeltaXA))) ,, (rationalNear , ((bound , (0<bound ,, (N , prBound))) ,, (bound2 , (0<bound2 ,, (N2 , prBound2)))))) = inverse x , ((deltaXAnd-A , (0<deltaXA ,, (NdeltaXA , λ m N<m → <WellDefined (Equivalence.transitive eq groupIsAbelian (Equivalence.transitive eq (Equivalence.symmetric eq +Associative) (+WellDefined (Equivalence.reflexive eq) (Equivalence.transitive eq groupIsAbelian (Equivalence.transitive eq (Equivalence.symmetric eq +Associative) (Equivalence.transitive eq (+WellDefined (Equivalence.reflexive eq) (cancel {m} (CauchyCompletion.elts a))) identRight)))))) (Equivalence.transitive eq +Associative (Equivalence.transitive eq (+WellDefined invRight (Equivalence.reflexive eq)) identLeft)) (orderRespectsAddition (prDeltaXA m N<m) (inverse x + (index (CauchyCompletion.elts a) m)))))) ,, (rationalNear , ((bound , (0<bound ,, (N , pr1))) ,, (bound2 , (0<bound2 ,, (N2 , prBound2))))))
where
cancel : {m : ℕ} (a : Sequence A) → (index (map inverse a) m) + (index a m) ∼ 0G
cancel {m} a rewrite equalityCommutative (mapAndIndex a inverse m) = invLeft
pr1 : (m : ℕ) → (N <N m) → (bound + index (apply _+_ (CauchyCompletion.elts a) (map inverse (constSequence (inverse x)))) m) < rationalNear
pr1 m N<m with prBound m N<m
... | bl rewrite indexAndApply (CauchyCompletion.elts a) (map inverse (constSequence (inverse x))) _+_ {m} | equalityCommutative (mapAndIndex (constSequence (inverse x)) inverse m) | indexAndConst x m | indexAndApply (constSequence x) (map inverse (map inverse (CauchyCompletion.elts a))) _+_ {m} | indexAndConst x m | equalityCommutative (mapAndIndex (map inverse (CauchyCompletion.elts a)) inverse m) | equalityCommutative (mapAndIndex (CauchyCompletion.elts a) inverse m) | indexAndConst (inverse x) m = <WellDefined (+WellDefined (Equivalence.reflexive eq) (Equivalence.transitive eq groupIsAbelian (+WellDefined (invTwice additiveGroup _) (Equivalence.symmetric eq (invTwice additiveGroup _))))) (Equivalence.reflexive eq) bl
boundModulus : (a : CauchyCompletion) → Sg A (λ b → Sg ℕ (λ N → (m : ℕ) → (N <N m) → (abs (index (CauchyCompletion.elts a) m)) < b))
boundModulus a with approximateBelow a 1R (0<1 (charNot2ImpliesNontrivial charNot2))
... | below , (below<a ,, a-below<e) with approximateAbove a 1R (0<1 (charNot2ImpliesNontrivial charNot2))
... | above , (a<above ,, above-a<e) with SetoidTotalOrder.totality tOrder 0R below
boundModulus a | below , (below<a ,, a-below<e) | above , (a<above ,, above-a<e) | inl (inl 0<below) with SetoidTotalOrder.totality tOrder 0R above
boundModulus a | below , ((belowBound , (0<belowBound ,, (Nbelow , prBelow))) ,, a-below<e) | above , ((bound , (0<bound ,, (N , ans))) ,, above-a<e) | inl (inl 0<below) | inl (inl 0<above) = above , ((N +N Nbelow) , λ m N<m → SetoidPartialOrder.transitive pOrder (res m N<m) (ans m (inequalityShrinkLeft N<m)))
where
res : (m : ℕ) → ((N +N Nbelow) <N m) → (abs (index (CauchyCompletion.elts a) m)) < (bound + index (CauchyCompletion.elts a) m)
res m N<m with SetoidTotalOrder.totality tOrder 0R (index (CauchyCompletion.elts a) m)
res m N<m | inl (inl _) = <WellDefined identLeft (Equivalence.reflexive eq) (orderRespectsAddition 0<bound (index (CauchyCompletion.elts a) m))
res m N<m | inl (inr am<0) = exFalso (irreflexive (SetoidPartialOrder.transitive pOrder 0<below (SetoidPartialOrder.transitive pOrder (SetoidPartialOrder.transitive pOrder (<WellDefined identLeft groupIsAbelian (orderRespectsAddition 0<belowBound below)) (prBelow m (inequalityShrinkRight N<m))) am<0)))
res m N<m | inr 0=am = <WellDefined 0=am (Equivalence.transitive eq (Equivalence.symmetric eq identRight) (+WellDefined (Equivalence.reflexive eq) 0=am)) 0<bound
boundModulus a | below , (below<a ,, a-below<e) | above , (a<above ,, above-a<e) | inl (inl 0<below) | inl (inr above<0) = exFalso (irreflexive (SetoidPartialOrder.transitive pOrder 0<below (SetoidPartialOrder.transitive pOrder (chain a below<a a<above) above<0)))
boundModulus a | below , (below<a ,, a-below<e) | above , (a<above ,, above-a<e) | inl (inl 0<below) | inr 0=above = exFalso (irreflexive (SetoidPartialOrder.transitive pOrder 0<below (<WellDefined (Equivalence.reflexive eq) (Equivalence.symmetric eq 0=above) (chain a below<a a<above))))
boundModulus a | below , (below<a ,, a-below<e) | above , (a<above ,, above-a<e) | inl (inr below<0) with SetoidTotalOrder.totality tOrder 0R above
boundModulus a | below , (below<a ,, a-below<e) | above , (a<above ,, above-a<e) | inl (inr below<0) | inl (inl 0<above) with SetoidTotalOrder.totality tOrder (inverse below) above
boundModulus a | below , ((boundBelow , (0<boundBelow ,, (N , prBoundBelow))) ,, a-below<e) | above , ((boundAbove , (0<boundAbove ,, (Nabove , prBoundAbove))) ,, above-a<e) | inl (inr below<0) | inl (inl 0<above) | inl (inl -bel<ab) = above , ((N +N Nabove) , ans)
where
ans : (m : ℕ) → (N +N Nabove <N m) → abs (index (CauchyCompletion.elts a) m) < above
ans m N<m with SetoidTotalOrder.totality tOrder 0G (index (CauchyCompletion.elts a) m)
ans m N<m | inl (inl 0<am) = SetoidPartialOrder.transitive pOrder (<WellDefined identLeft (Equivalence.reflexive eq) (orderRespectsAddition 0<boundAbove (index (CauchyCompletion.elts a) m))) (prBoundAbove m (inequalityShrinkRight N<m))
ans m N<m | inl (inr am<0) = SetoidPartialOrder.transitive pOrder (ringSwapNegatives' (prBoundBelow m (inequalityShrinkLeft N<m))) (SetoidPartialOrder.transitive pOrder (ringSwapNegatives' (<WellDefined identLeft groupIsAbelian (orderRespectsAddition 0<boundBelow below))) -bel<ab)
ans m N<m | inr 0=am = <WellDefined 0=am (Equivalence.reflexive eq) 0<above
boundModulus a | below , ((boundBelow , (0<boundBelow ,, (N , prBoundBelow))) ,, a-below<e) | above , ((boundAbove , (0<boundAbove ,, (Nabove , prBoundAbove))) ,, above-a<e) | inl (inr below<0) | inl (inl 0<above) | inl (inr ab<-bel) = inverse below , ((N +N Nabove) , ans)
where
ans : (m : ℕ) → (N +N Nabove <N m) → abs (index (CauchyCompletion.elts a) m) < (inverse below)
ans m N<m with SetoidTotalOrder.totality tOrder 0G (index (CauchyCompletion.elts a) m)
ans m N<m | inl (inl 0<am) = SetoidPartialOrder.transitive pOrder (SetoidPartialOrder.transitive pOrder (<WellDefined identLeft (Equivalence.reflexive eq) (orderRespectsAddition 0<boundAbove (index (CauchyCompletion.elts a) m))) (prBoundAbove m (inequalityShrinkRight N<m))) ab<-bel
ans m N<m | inl (inr am<0) = ringSwapNegatives' (SetoidPartialOrder.transitive pOrder (<WellDefined identLeft groupIsAbelian (orderRespectsAddition 0<boundBelow below)) (prBoundBelow m (inequalityShrinkLeft N<m)))
ans m N<m | inr 0=am = <WellDefined 0=am (Equivalence.reflexive eq) (lemm2 below below<0)
boundModulus a | below , ((boundBelow , (0<boundBelow ,, (N , prBoundBelow))) ,, a-below<e) | above , ((boundAbove , (0<boundAbove ,, (Nabove , prBoundAbove))) ,, above-a<e) | inl (inr below<0) | inl (inl 0<above) | inr -bel=ab = above , ((N +N Nabove) , ans)
where
ans : (m : ℕ) → (N +N Nabove <N m) → abs (index (CauchyCompletion.elts a) m) < above
ans m N<m with SetoidTotalOrder.totality tOrder 0G (index (CauchyCompletion.elts a) m)
ans m N<m | inl (inl 0<am) = SetoidPartialOrder.transitive pOrder (<WellDefined identLeft (Equivalence.reflexive eq) (orderRespectsAddition 0<boundAbove (index (CauchyCompletion.elts a) m))) (prBoundAbove m (inequalityShrinkRight N<m))
ans m N<m | inl (inr am<0) = <WellDefined (Equivalence.reflexive eq) (-bel=ab) (ringSwapNegatives' (SetoidPartialOrder.transitive pOrder (<WellDefined identLeft groupIsAbelian (orderRespectsAddition 0<boundBelow below)) (prBoundBelow m (inequalityShrinkLeft N<m))))
ans m N<m | inr 0=am = <WellDefined 0=am (Equivalence.reflexive eq) 0<above
boundModulus a | below , ((boundBelow , (0<boundBelow ,, (N , prBoundBelow))) ,, a-below<e) | above , ((boundAbove , (0<boundAbove ,, (Nabove , prBoundAbove))) ,, above-a<e) | inl (inr below<0) | inl (inr above<0) = inverse below , ((N +N Nabove) , ans)
where
ans : (m : ℕ) → ((N +N Nabove) <N m) → abs (index (CauchyCompletion.elts a) m) < inverse below
ans m N<m with SetoidTotalOrder.totality tOrder 0R (index (CauchyCompletion.elts a) m)
ans m N<m | inl (inl 0<am) = exFalso (irreflexive {0G} (SetoidPartialOrder.transitive pOrder 0<am (SetoidPartialOrder.transitive pOrder (SetoidPartialOrder.transitive pOrder (<WellDefined identLeft (Equivalence.reflexive eq) (orderRespectsAddition 0<boundAbove (index (CauchyCompletion.elts a) m))) (prBoundAbove m (inequalityShrinkRight N<m))) above<0)))
ans m N<m | inl (inr am<0) = ringSwapNegatives' (SetoidPartialOrder.transitive pOrder (<WellDefined identLeft groupIsAbelian (orderRespectsAddition 0<boundBelow below)) (prBoundBelow m (inequalityShrinkLeft N<m)))
ans m N<m | inr 0=am = exFalso (irreflexive {0G} (<WellDefined (Equivalence.symmetric eq 0=am) (Equivalence.reflexive eq) (SetoidPartialOrder.transitive pOrder (SetoidPartialOrder.transitive pOrder (<WellDefined identLeft (Equivalence.reflexive eq) (orderRespectsAddition 0<boundAbove (index (CauchyCompletion.elts a) m))) (prBoundAbove m (inequalityShrinkRight N<m))) above<0)))
boundModulus a | below , ((boundBelow , (0<boundBelow ,, (N , prBoundBelow))) ,, a-below<e) | above , ((boundAbove , (0<boundAbove ,, (Nabove , prBoundAbove))) ,, above-a<e) | inl (inr below<0) | inr 0=above = inverse below , ((N +N Nabove) , ans)
where
ans : (m : ℕ) → ((N +N Nabove) <N m) → abs (index (CauchyCompletion.elts a) m) < inverse below
ans m N<m with SetoidTotalOrder.totality tOrder 0R (index (CauchyCompletion.elts a) m)
ans m N<m | inl (inl 0<am) = exFalso (irreflexive {0G} (<WellDefined (Equivalence.reflexive eq) (Equivalence.symmetric eq 0=above) (SetoidPartialOrder.transitive pOrder 0<am (SetoidPartialOrder.transitive pOrder (<WellDefined identLeft (Equivalence.reflexive eq) (orderRespectsAddition 0<boundAbove (index (CauchyCompletion.elts a) m))) (prBoundAbove m (inequalityShrinkRight N<m))))))
ans m N<m | inl (inr am<0) = ringSwapNegatives' (SetoidPartialOrder.transitive pOrder (<WellDefined identLeft groupIsAbelian (orderRespectsAddition 0<boundBelow below)) (prBoundBelow m (inequalityShrinkLeft N<m)))
ans m N<m | inr 0=am = <WellDefined 0=am (Equivalence.reflexive eq) (lemm2 _ below<0)
boundModulus a | below , ((boundBelow , ((boundBelowDiff ,, (Nb , ansBelow)))) ,, a-below<e) | above , ((bound , (0<bound ,, (N , ans))) ,, above-a<e) | inr 0=below = above , ((N +N Nb) , λ m N<m → SetoidPartialOrder.transitive pOrder (res m N<m) (ans m (inequalityShrinkLeft N<m)))
where
res : (m : ℕ) → (N +N Nb) <N m → (abs (index (CauchyCompletion.elts a) m)) < (bound + index (CauchyCompletion.elts a) m)
res m N<m with SetoidTotalOrder.totality tOrder 0R (index (CauchyCompletion.elts a) m)
res m N<m | inl (inl 0<am) = <WellDefined identLeft (Equivalence.reflexive eq) (orderRespectsAddition 0<bound (index (CauchyCompletion.elts a) m))
res m N<m | inl (inr am<0) = exFalso (irreflexive (<WellDefined (Equivalence.symmetric eq 0=below) (Equivalence.reflexive eq) (SetoidPartialOrder.transitive pOrder (SetoidPartialOrder.transitive pOrder (<WellDefined identLeft groupIsAbelian (orderRespectsAddition boundBelowDiff below)) (ansBelow m (inequalityShrinkRight N<m))) am<0)))
res m N<m | inr 0=am = <WellDefined 0=am (Equivalence.transitive eq (Equivalence.symmetric eq identRight) (+WellDefined (Equivalence.reflexive eq) 0=am)) 0<bound
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