agdaproofs/Numbers/Primes/PrimeNumbers.agda

{-# OPTIONS --warning=error --safe --without-K #-}

open import LogicalFormulae
open import Numbers.Naturals.Definition
open import Numbers.Naturals.Semiring
open import Numbers.Naturals.Naturals
open import Numbers.Naturals.Order
open import Numbers.Naturals.Order.Lemmas
open import Numbers.Naturals.Order.WellFounded
open import KeyValue.KeyValue
open import Orders.Total.Definition
open import Orders.Partial.Definition
open import Vectors
open import Maybe
open import Semirings.Definition
open import Numbers.Naturals.EuclideanAlgorithm

module Numbers.Primes.PrimeNumbers where

open TotalOrder ℕTotalOrder
open Semiring ℕSemiring
open import Decidable.Lemmas ℕDecideEquality

dividesEqualityLemma'' : {a b : ℕ} → (quot1 quot2 : ℕ) → .(quot1 ≡ quot2) → (rem : ℕ) → .(pr1 : (quot1 +N a *N quot1) +N rem ≡ b) → .(pr2 : (quot2 +N a *N quot2) +N rem ≡ b) → (y : rem <N' succ a) → (x1 : zero <N' succ a) → _≡_ {A = divisionAlgResult' _ _} record { quot = quot1 ; rem = rem ; pr = pr1 ; remIsSmall = inl y ; quotSmall = inl x1 } record { quot = quot2 ; rem = rem ; pr = pr2 ; remIsSmall = inl y ; quotSmall = inl x1}
dividesEqualityLemma'' {a} {b} q1 q2 pr rem pr1 pr2 y x1 with squashN record { eq = pr }
... | refl = refl

dividesEqualityLemma' : {a b : ℕ} → (quot1 quot2 : ℕ) → (rem : ℕ) → .(pr1 : (quot1 +N a *N quot1) +N rem ≡ b) → .(pr2 : (quot2 +N a *N quot2) +N rem ≡ b) → (y : rem <N' succ a) → (y2 : rem <N' succ a) → (x1 : zero <N' succ a) → _≡_ {A = divisionAlgResult' _ _} record { quot = quot1 ; rem = rem ; pr = pr1 ; remIsSmall = inl y ; quotSmall = inl x1 } record { quot = quot2 ; rem = rem ; pr = pr2 ; remIsSmall = inl y2 ; quotSmall = inl x1}
dividesEqualityLemma' {a} {b} quot1 quot2 rem pr1 pr2 y y2 x1 with productCancelsLeft (succ a) quot2 quot1 (succIsPositive a) (canSubtractFromEqualityRight (transitivity (squashN record { eq = pr2 }) (equalityCommutative (squashN record { eq = pr1 }))))
... | refl with <N'Refl y y2
... | refl = refl

dividesEqualityLemma : {a b : ℕ} → (quot1 quot2 : ℕ) → (rem1 rem2 : ℕ) → .(pr1 : (quot1 +N a *N quot1) +N rem1 ≡ b) → .(pr2 : (quot2 +N a *N quot2) +N rem2 ≡ b) → .(rem1 ≡ rem2) → (y : rem1 <N' succ a) → (y2 : rem2 <N' succ a) → (x1 : zero <N' succ a) → _≡_ {A = divisionAlgResult' _ _} record { quot = quot1 ; rem = rem1 ; pr = pr1 ; remIsSmall = inl y ; quotSmall = inl x1 } record { quot = quot2 ; rem = rem2 ; pr = pr2 ; remIsSmall = inl y2 ; quotSmall = inl x1}
dividesEqualityLemma {a} {b} quot1 quot2 rem1 rem2 pr1 pr2 remEq y y2 x1 with squashN record { eq = remEq }
... | refl = dividesEqualityLemma' quot1 quot2 rem1 pr1 pr2 y y2 x1

dividesEqualityLemma1 : {a b : ℕ} → (quot1 quot2 : ℕ) → (rem1 rem2 : ℕ) → .(pr1 : (quot1 +N a *N quot1) +N rem1 ≡ b) → .(pr2 : (quot2 +N a *N quot2) +N rem2 ≡ b) → .(rem1 ≡ rem2) → (y : (rem1 <N' succ a) || (succ a =N' zero)) → (y2 : (rem2 <N' succ a) || (succ a =N' zero)) → (x1 : zero <N' succ a) → _≡_ {A = divisionAlgResult' _ _} record { quot = quot1 ; rem = rem1 ; pr = pr1 ; remIsSmall = y ; quotSmall = inl x1 } record { quot = quot2 ; rem = rem2 ; pr = pr2 ; remIsSmall = y2 ; quotSmall = inl x1}
dividesEqualityLemma1 {a} {b} quot1 quot2 rem1 rem2 pr1 pr2 remEq (inl x) (inl y) x1 = dividesEqualityLemma quot1 quot2 rem1 rem2 pr1 pr2 remEq x y x1

dividesEqualityLemma2 : {a b : ℕ} → (quot1 quot2 : ℕ) → (rem1 rem2 : ℕ) → .(pr1 : (quot1 +N a *N quot1) +N rem1 ≡ b) → .(pr2 : (quot2 +N a *N quot2) +N rem2 ≡ b) → .(rem1 ≡ rem2) → (y : (rem1 <N' succ a) || (succ a =N' zero)) → (y2 : (rem2 <N' succ a) || (succ a =N' zero)) → (x1 : zero <N' succ a) (x2 : zero <N' succ a) → _≡_ {A = divisionAlgResult' _ _} record { quot = quot1 ; rem = rem1 ; pr = pr1 ; remIsSmall = y ; quotSmall = inl x1 } record { quot = quot2 ; rem = rem2 ; pr = pr2 ; remIsSmall = y2 ; quotSmall = inl x2 }
dividesEqualityLemma2 {a} {b} quot1 quot2 rem1 rem2 pr1 pr2 remEq x y x1 x2 with <N'Refl x1 x2
... | refl = dividesEqualityLemma1 quot1 quot2 rem1 rem2 pr1 pr2 remEq x y x1

dividesEqualityLemma3 : {a b : ℕ} → (quot1 quot2 : ℕ) → (rem1 rem2 : ℕ) → .(pr1 : (succ a *N quot1) +N rem1 ≡ b) → .(pr2 : (succ a *N quot2) +N rem2 ≡ b) → .(rem1 ≡ rem2) → (y : (rem1 <N' succ a) || (succ a =N' zero)) → (y2 : (rem2 <N' succ a) || (succ a =N' zero)) → (x1 : (zero <N' succ a) || (zero =N' succ a) && (quot1 =N' zero)) (x2 : (zero <N' succ a) || (zero =N' succ a) && (quot2 =N' zero)) → _≡_ {A = divisionAlgResult' _ _} record { quot = quot1 ; rem = rem1 ; pr = pr1 ; remIsSmall = y ; quotSmall = x1 } record { quot = quot2 ; rem = rem2 ; pr = pr2 ; remIsSmall = y2 ; quotSmall = x2 }
dividesEqualityLemma3 {a} {b} quot1 quot2 rem1 rem2 pr1 pr2 remEq x y (inl x1) (inl x2) = dividesEqualityLemma2 quot1 quot2 rem1 rem2 pr1 pr2 remEq x y x1 x2

dividesEqualityPr' : {a b : ℕ} → (res1 res2 : divisionAlgResult' a b) → res1 ≡ res2
dividesEqualityPr' {zero} {zero} record { quot = quot₁ ; rem = rem₁ ; pr = pr1 ; remIsSmall = (inr f2) ; quotSmall = (inr (f4 ,, quot1=0)) } record { quot = quot ; rem = rem ; pr = pr ; remIsSmall = (inr f1) ; quotSmall = (inr (f3 ,, quot=0)) } with squashN quot1=0
... | refl with squashN quot=0
... | refl with =N'Refl f1 f2
... | refl with =N'Refl f3 f4
... | refl with =N'Refl quot1=0 quot=0
... | refl with transitivity (squashN record { eq = pr }) (equalityCommutative (squashN record { eq = pr1 }))
... | refl = refl
dividesEqualityPr' {zero} {succ b} record { quot = quot1 ; rem = rem1 ; pr = pr1 ; remIsSmall = (inr rSm) ; quotSmall = (inr (f ,, quot1=0)) } record { quot = quot ; rem = rem ; pr = pr ; remIsSmall = (inr rSm2) ; quotSmall = (inr (f2 ,, quot=0)) } with squashN quot=0
... | refl with squashN quot1=0
... | refl with =N'Refl rSm rSm2
... | refl with =N'Refl quot1=0 quot=0
... | refl with =N'Refl f f2
... | refl with transitivity (squashN record { eq = pr }) (equalityCommutative (squashN record { eq = pr1 }))
... | refl = refl
dividesEqualityPr' {succ a} {zero} record { quot = quot1 ; rem = rem1 ; pr = pr1 ; remIsSmall = (inl remSm) ; quotSmall = (inl qSm) } record { quot = quot ; rem = rem ; pr = pr ; remIsSmall = (inl remSm2) ; quotSmall = (inl qSm2) } with sumZeroImpliesSummandsZero {quot +N a *N quot} {rem} (squashN record { eq = pr })
... | fst ,, refl with sumZeroImpliesSummandsZero {quot} {_} fst
... | refl ,, _ with sumZeroImpliesSummandsZero {_} {rem1} (squashN record { eq = pr1 })
... | fst2 ,, refl with sumZeroImpliesSummandsZero {quot1} {_} fst2
... | refl ,, _ with <N'Refl remSm remSm2
... | refl with <N'Refl qSm qSm2
... | refl = refl
dividesEqualityPr' {succ a} {succ b} record { quot = quot1 ; rem = rem1 ; pr = pr1 ; remIsSmall = inl remIsSmall1 ; quotSmall = inl (quotSmall1) } record { quot = quot ; rem = rem ; pr = pr ; remIsSmall = inl remIsSmall ; quotSmall = (inl quotSmall) } = dividesEqualityLemma3 quot1 quot rem1 rem pr1 pr t (inl remIsSmall1) (inl remIsSmall) (inl quotSmall1) (inl quotSmall)
  where
    t : rem1 ≡ rem
    t = modIsUnique record { quot = quot1 ; rem = rem1 ; pr = squash pr1 ; remIsSmall = inl (<N'To<N remIsSmall1) ; quotSmall = inl (<N'To<N quotSmall) } record { quot = quot ; rem = rem ; pr = squash pr ; remIsSmall = inl (<N'To<N remIsSmall) ; quotSmall = inl (<N'To<N quotSmall1) }

dividesEquality : {a b : ℕ} → (res1 res2 : a ∣' b) → res1 ≡ res2
dividesEquality (divides' res1 x1) (divides' res2 x2) with dividesEqualityPr' res1 res2
... | refl = refl

data notDiv : ℕ → ℕ → Set where
  doesNotDivide : {a b : ℕ} → (res : divisionAlgResult a b) → 0 <N divisionAlgResult.rem res → notDiv a b

twoDividesFour : succ (succ zero) ∣ succ (succ (succ (succ zero)))
twoDividesFour = divides {(succ (succ zero))} {succ (succ (succ (succ zero)))} (record { quot = succ (succ zero) ; rem = zero ; pr = refl ; remIsSmall = inl (succIsPositive 1) ; quotSmall = inl (succIsPositive 1) }) refl

record Prime (p : ℕ) : Set where
  field
    p>1 : 1 <N p
    pr : forall {i : ℕ} → i ∣ p → i <N p → zero <N i → i ≡ (succ zero)

record Composite (n : ℕ) : Set where
  field
    n>1 : 1 <N n
    divisor : ℕ
    dividesN : divisor ∣ n
    divisorLessN : divisor <N n
    divisorNot1 : 1 <N divisor
    divisorPrime : Prime divisor
    noSmallerDivisors : ∀ i → i <N divisor → 1 <N i → i ∣ n → False

notBothPrimeAndComposite : {n : ℕ} → Composite n → Prime n → False
notBothPrimeAndComposite {n} record { n>1 = n>1 ; divisor = divisor ; dividesN = dividesN ; divisorLessN = divisorLessN ; divisorNot1 = divisorNot1 } record { p>1 = p>1 ; pr = pr } = lessImpliesNotEqual divisorNot1 (equalityCommutative div=1)
  where
    div=1 : divisor ≡ 1
    div=1 = pr {divisor} dividesN divisorLessN (TotalOrder.<Transitive ℕTotalOrder (succIsPositive 0) divisorNot1)

zeroIsNotPrime : Prime 0 → False
zeroIsNotPrime record { p>1 = p>1 ; pr = pr } = zeroNeverGreater p>1

oneIsNotPrime : Prime 1 → False
oneIsNotPrime record { p>1 = (le x proof) ; pr = pr } = naughtE (equalityCommutative absurd')
  where
    absurd : x +N 1 ≡ 0
    absurd = succInjective proof
    absurd' : succ x ≡ 0
    absurd' rewrite Semiring.commutative ℕSemiring 1 x = absurd

twoIsPrime : Prime 2
Prime.p>1 twoIsPrime = succPreservesInequality (succIsPositive 0)
Prime.pr twoIsPrime {i} i|2 i<2 0<i with totality i (succ (succ zero))
Prime.pr twoIsPrime {zero} i|2 i<2 (le x ()) | order
Prime.pr twoIsPrime {succ zero} i|2 i<2 0<i | order = refl
Prime.pr twoIsPrime {succ (succ zero)} i|2 i<2 0<i | order = exFalso (lessImpliesNotEqual {2} i<2 refl)
Prime.pr twoIsPrime {succ (succ (succ i))} i|2 i<2 0<i | inl (inl x) = exFalso (TotalOrder.irreflexive ℕTotalOrder (TotalOrder.<Transitive ℕTotalOrder i<2 (succPreservesInequality (succPreservesInequality (succIsPositive i)))))
Prime.pr twoIsPrime {succ (succ (succ i))} i|2 i<2 0<i | inl (inr twoLessThree) = exFalso (TotalOrder.irreflexive ℕTotalOrder (TotalOrder.<Transitive ℕTotalOrder twoLessThree i<2))
Prime.pr twoIsPrime {succ (succ (succ i))} i|2 i<2 0<i | inr ()

threeIsPrime : Prime 3
Prime.p>1 threeIsPrime = le 1 refl
Prime.pr threeIsPrime {succ zero} i|3 i<3 _ = refl
Prime.pr threeIsPrime {succ (succ zero)} (divides record { quot = (succ (succ (succ zero))) ; rem = zero ; pr = () ; remIsSmall = remIsSmall ; quotSmall = quotSmall } x) i<3 _
Prime.pr threeIsPrime {succ (succ zero)} (divides record { quot = (succ (succ (succ (succ quot)))) ; rem = zero ; pr = () ; remIsSmall = remIsSmall ; quotSmall = quotSmall } x) i<3 _
Prime.pr threeIsPrime {succ (succ (succ i))} i|3 (le (succ (succ zero)) ()) _
Prime.pr threeIsPrime {succ (succ (succ i))} i|3 (le (succ (succ (succ x))) ()) _

compositeImpliesNotPrime : (m p : ℕ) → (succ zero <N m) → (m <N p) → (m ∣ p) → Prime p → False
compositeImpliesNotPrime zero p (le x ()) _ mDivP pPrime
compositeImpliesNotPrime (succ zero) p mLarge _ mDivP pPrime = lessImpliesNotEqual {succ zero} {succ zero} mLarge refl
compositeImpliesNotPrime (succ (succ m)) zero _ _ mDivP ()
compositeImpliesNotPrime (succ (succ m)) (succ zero) _ _ mDivP primeP = exFalso (oneIsNotPrime primeP)
compositeImpliesNotPrime (succ (succ m)) (succ (succ p)) _ mLessP mDivP pPrime = false
  where
    r = succ (succ m)
    q = succ (succ p)
    rEqOne : r ≡ succ zero
    rEqOne = (Prime.pr pPrime) {r} mDivP mLessP (succIsPositive (succ m))
    false : False
    false = succIsNonzero (succInjective rEqOne)

fourIsNotPrime : Prime 4 → False
fourIsNotPrime = compositeImpliesNotPrime (succ (succ zero)) (succ (succ (succ (succ zero)))) (le zero refl) (le (succ zero) refl) twoDividesFour

record Coprime (a : ℕ) (b : ℕ) : Set where
  field
    hcf : hcfData a b
    hcfNot1 : 1 <N hcfData.c hcf

record numberLessThan (n : ℕ) : Set where
  field
    a : ℕ
    a<n : a <N' n
  upper : ℕ
  upper = n

numberLessThanEquality : {n : ℕ} → (a b : numberLessThan n) → (numberLessThan.a a ≡ numberLessThan.a b) → a ≡ b
numberLessThanEquality record { a = a ; a<n = a<n } record { a = b ; a<n = b<n } pr rewrite pr | <N'Refl a<n b<n = refl

numberLessThanOrder : (n : ℕ) → TotalOrder (numberLessThan n)
PartialOrder._<_ (TotalOrder.order (numberLessThanOrder n)) = λ a b → (numberLessThan.a a) <N numberLessThan.a b
PartialOrder.irreflexive (TotalOrder.order (numberLessThanOrder n)) pr = TotalOrder.irreflexive ℕTotalOrder pr
PartialOrder.<Transitive (TotalOrder.order (numberLessThanOrder n)) pr1 pr2 = TotalOrder.<Transitive ℕTotalOrder pr1 pr2
TotalOrder.totality (numberLessThanOrder n) a b with totality (numberLessThan.a a) (numberLessThan.a b)
TotalOrder.totality (numberLessThanOrder n) a b | inl (inl x) = inl (inl x)
TotalOrder.totality (numberLessThanOrder n) a b | inl (inr x) = inl (inr x)
TotalOrder.totality (numberLessThanOrder n) a b | inr x rewrite x = inr (numberLessThanEquality a b x)

numberLessThanInject : {newMax : ℕ} → (max : ℕ) → (n : numberLessThan max) → (max <N newMax) → (numberLessThan newMax)
numberLessThanInject max record { a = n ; a<n = n<max } max<newMax = record { a = n ; a<n = <NTo<N' (PartialOrder.<Transitive (TotalOrder.order ℕTotalOrder) (<N'To<N n<max) max<newMax) }

numberLessThanInjectComp : {max : ℕ} (a b : ℕ) → (i : numberLessThan b) → (pr : b <N a) → (pr2 : a <N max) → numberLessThanInject {max} a (numberLessThanInject {a} b i pr) pr2 ≡ numberLessThanInject {max} b i (PartialOrder.<Transitive (TotalOrder.order ℕTotalOrder) pr pr2)
numberLessThanInjectComp {max} a b record { a = i ; a<n = i<max } b<a a<max = numberLessThanEquality _ _ refl

allNumbersLessThanDescending : (n : ℕ) → Vec (numberLessThan n) n
allNumbersLessThanDescending zero = []
allNumbersLessThanDescending (succ n) = record { a = n ; a<n = <NTo<N' (le zero refl) } ,- vecMap (λ i → numberLessThanInject {succ n} (numberLessThan.upper i) i (le zero refl)) (allNumbersLessThanDescending n)

allNumbersLessThan : (n : ℕ) → Vec (numberLessThan n) n
allNumbersLessThan n = vecRev (allNumbersLessThanDescending n)

maxDivides : (a b : ℕ) → ((TotalOrder.max ℕTotalOrder a b) ∣ a) → (TotalOrder.max ℕTotalOrder a b) ∣ b → (((a ≡ 0) && (0 <N b)) || ((b ≡ 0) && (0 <N a))) || (a ≡ b)
maxDivides a b max|a max|b with totality a b
maxDivides a b max|a max|b | inl (inl a<b) = inl (inl (record { fst = gg ; snd = identityOfIndiscernablesLeft _<N_ a<b gg}))
  where
    gg : a ≡ 0
    gg = biggerThanCantDivideLemma {a} {b} a<b max|a
maxDivides a b max|a max|b | inl (inr b<a) = inl (inr (record { fst = gg ; snd = identityOfIndiscernablesLeft _<N_ b<a gg }))
  where
    gg : b ≡ 0
    gg = biggerThanCantDivideLemma b<a max|b
maxDivides a .a a|max b|max | inr refl = inr refl

{-
hcfsEquivalent' : {a b : ℕ} → extensionalHCF a b → hcfData a b
hcfData.c (hcfsEquivalent' {a} {b} record { c = c ; c|a = c|a ; c|b = c|b ; hcfExtension = hcfExtension }) = c
hcfData.c|a (hcfsEquivalent' {a} {b} record { c = c ; c|a = c|a ; c|b = c|b ; hcfExtension = hcfExtension }) = c|a
hcfData.c|b (hcfsEquivalent' {a} {b} record { c = c ; c|a = c|a ; c|b = c|b ; hcfExtension = hcfExtension }) = c|b
hcfData.hcf (hcfsEquivalent' {a} {b} record { c = c ; c|a = c|a ; c|b = c|b ; hcfExtension = hcfExtension }) x x|a x|b with totality ℕTotalOrder x c
hcfData.hcf (hcfsEquivalent' {a} {b} record { c = c ; c|a = c|a ; c|b = c|b ; zeroCase = zeroCase ; hcfExtension = hcfExtension ; hcfExtensionIsRightLength = hIRL }) x x|a x|b | inl (inl x<c) = {!!}
  where
    xLess : numberLessThan c
    xLess = record { a = x ; a<n = x<c }
    pair : Set
    pair = Sg (numberLessThan c) (λ i → (notDiv (numberLessThan.a i) a || notDiv (numberLessThan.a i) b) || (numberLessThan.a i ∣ a) & numberLessThan.a i ∣ b & (numberLessThan.a i ∣ c))
    pr : Sg pair λ p → (lookup (MapWithDomain.map hcfExtension) xLess ≡ {!!})
    pr = MapWithDomain.lookup' hcfExtension xLess (hcfsContains {a} {b} {x} (record { c = c ; c|a = c|a ; c|b = c|b ; zeroCase = zeroCase ; hcfExtension = hcfExtension ; hcfExtensionIsRightLength = hIRL }) x<c)
hcfData.hcf (hcfsEquivalent' {a} {b} record { c = c ; c|a = c|a ; c|b = c|b ; zeroCase = _ ; hcfExtension = hcfExtension ; hcfExtensionIsRightLength = _ }) x x|a x|b | inl (inr c<x) = {!!}
hcfData.hcf (hcfsEquivalent' {a} {b} record { c = c ; c|a = c|a ; c|b = c|b ; zeroCase = _ ; hcfExtension = hcfExtension ; hcfExtensionIsRightLength = _ }) x x|a x|b | inr x=c rewrite x=c = aDivA c

extensionalHCFEquality : {a b : ℕ} → {h1 h2 : extensionalHCF a b} → (extensionalHCF.c h1 ≡ extensionalHCF.c h2) → h1 ≡ h2
extensionalHCFEquality {a} {b} {record { c = c1 ; c|a = c|a1 ; c|b = c|b1 ; hcfExtension = hcfExtension1 }} {record { c = c2 ; c|a = c|a2 ; c|b = c|b2 ; hcfExtension = hcfExtension2 }} pr rewrite pr = {!!}
-}

divisorIsSmaller : {a b : ℕ} → a ∣ succ b → succ b <N a → False
divisorIsSmaller {a} {b} (divides record { quot = zero ; rem = .0 ; pr = pr } refl) sb<a rewrite Semiring.sumZeroRight ℕSemiring (a *N zero) = go
  where
    go : False
    go rewrite Semiring.productZeroRight ℕSemiring a = naughtE pr
divisorIsSmaller {a} {b} (divides record { quot = (succ quot) ; rem = .0 ; pr = pr } refl) sb<a rewrite Semiring.sumZeroRight ℕSemiring (a *N succ quot) = go
  where
    go : False
    go rewrite equalityCommutative pr = go'
      where
        go' : False
        go' rewrite multiplicationNIsCommutative a (succ quot) = cannotAddAndEnlarge' sb<a

primeDivisorIs1OrP : {a p : ℕ} → (prime : Prime p) → (a ∣ p) → (a ≡ 1) || (a ≡ p)
primeDivisorIs1OrP {zero} {zero} prime a|p = inr refl
primeDivisorIs1OrP {zero} {succ p} prime a|p = exFalso (zeroDividesNothing p a|p)
primeDivisorIs1OrP {succ zero} {p} prime a|p = inl refl
primeDivisorIs1OrP {succ (succ a)} {p} prime a|p with totality (succ (succ a)) p
primeDivisorIs1OrP {succ (succ a)} {p} prime a|p | inl (inl ssa<p) = go p prime a|p ssa<p
  where
    go : (n : ℕ) → Prime n → succ (succ a) ∣ n → succ (succ a) <N n → (succ (succ a) ≡ 1) || (succ (succ a) ≡ p)
    go zero pr x|n n<n = exFalso (zeroIsNotPrime pr)
    go (succ zero) pr x|n n<n = exFalso (oneIsNotPrime pr)
    go (succ (succ n)) pr x|n n<n = inl ((Prime.pr pr) {succ (succ a)} x|n n<n (succIsPositive (succ a)))
primeDivisorIs1OrP {succ (succ a)} {zero} prime a|p | inl (inr x) = exFalso (zeroIsNotPrime prime)
primeDivisorIs1OrP {succ (succ a)} {succ p} prime a|p | inl (inr x) = exFalso (divisorIsSmaller {succ (succ a)} {p} a|p x)
primeDivisorIs1OrP {succ (succ a)} {p} prime a|p | inr x = inr x

hcfPrimeIsOne' : {p : ℕ} → {a : ℕ} → (Prime p) → (0 <N divisionAlgResult.rem (divisionAlg p a)) → (extendedHcf.c (euclid a p) ≡ 1) || (extendedHcf.c (euclid a p) ≡ p)
hcfPrimeIsOne' {p} {a} pPrime pCoprimeA with euclid a p
hcfPrimeIsOne' {p} {a} pPrime pCoprimeA | record { hcf = record { c = hcf ; c|a = hcf|a ; c|b = hcf|p ; hcf = hcfPr } } with divisionAlg p a
hcfPrimeIsOne' {p} {a} pPrime pCoprimeA | record { hcf = record { c = hcf ; c|a = hcf|a ; c|b = hcf|p ; hcf = hcfPr } } | record { quot = quot ; rem = rem ; pr = prPDivA } with primeDivisorIs1OrP pPrime hcf|p
hcfPrimeIsOne' {p} {a} pPrime pCoprimeA | record { hcf = record { c = hcf ; c|a = hcf|a ; c|b = hcf|p ; hcf = hcfPr } } | record { quot = quot ; rem = rem ; pr = prPDivA } | inl x = inl x
hcfPrimeIsOne' {p} {a} pPrime pCoprimeA | record { hcf = record { c = hcf ; c|a = hcf|a ; c|b = hcf|p ; hcf = hcfPr } } | record { quot = quot ; rem = rem ; pr = prPDivA } | inr x = inr x

divisionDecidable : (a b : ℕ) → (a ∣ b) || ((a ∣ b) → False)
divisionDecidable zero zero = inl (aDivA zero)
divisionDecidable zero (succ b) = inr f
  where
    f : zero ∣ succ b → False
    f (divides record { quot = quot ; rem = rem ; pr = pr ; remIsSmall = remIsSmall } x) rewrite x = naughtE pr
divisionDecidable (succ a) b with divisionAlg (succ a) b
divisionDecidable (succ a) b | record { quot = quot ; rem = zero ; pr = pr ; remIsSmall = remSmall } = inl (divides (record { quot = quot ; rem = zero ; pr = pr ; remIsSmall = remSmall ; quotSmall = inl (succIsPositive a) }) refl)
divisionDecidable (succ a) b | record { quot = b/a ; rem = succ rem ; pr = prANotDivB ; remIsSmall = inr p } = exFalso (naughtE (equalityCommutative p))
divisionDecidable (succ a) b | record { quot = b/a ; rem = succ rem ; pr = prANotDivB ; remIsSmall = inl p } = inr f
  where
    f : (succ a) ∣ b → False
    f (divides record { quot = b/a' ; rem = .0 ; pr = pr } refl) rewrite Semiring.sumZeroRight ℕSemiring ((succ a) *N b/a') = naughtE (modUniqueLemma {zero} {succ rem} {succ a} b/a' b/a (succIsPositive a) p comp')
      where
        comp : (succ a) *N b/a' ≡ (succ a) *N b/a +N succ rem
        comp = transitivity pr (equalityCommutative prANotDivB)
        comp' : (succ a) *N b/a' +N zero ≡ (succ a) *N b/a +N succ rem
        comp' rewrite Semiring.sumZeroRight ℕSemiring (succ a *N b/a') = comp

doesNotDivideImpliesNonzeroRem : (a b : ℕ) → ((a ∣ b) → False) → 0 <N divisionAlgResult.rem (divisionAlg a b)
doesNotDivideImpliesNonzeroRem a b pr with divisionAlg a b
doesNotDivideImpliesNonzeroRem a b pr | record { quot = quot ; rem = rem ; pr = divAlgPr ; remIsSmall = remIsSmall } with zeroIsValidRem rem
doesNotDivideImpliesNonzeroRem a b pr | record { quot = quot ; rem = rem ; pr = divAlgPr ; remIsSmall = remIsSmall } | inl x = x
doesNotDivideImpliesNonzeroRem a b pr | record { quot = quot ; rem = rem ; pr = divAlgPr ; remIsSmall = remIsSmall ; quotSmall = quotSmall } | inr x = exFalso (pr aDivB)
  where
    aDivB : a ∣ b
    aDivB = divides (record { quot = quot ; rem = rem ; pr = divAlgPr ; remIsSmall = remIsSmall ; quotSmall = quotSmall }) x

hcfPrimeIsOne : {p : ℕ} → {a : ℕ} → (Prime p) → ((p ∣ a) → False) → extendedHcf.c (euclid a p) ≡ 1
hcfPrimeIsOne {p} {a} pPrime pr with hcfPrimeIsOne' {p} {a} pPrime (doesNotDivideImpliesNonzeroRem p a pr)
hcfPrimeIsOne {p} {a} pPrime pr | inl x = x
hcfPrimeIsOne {p} {a} pPrime pr | inr x with euclid a p
hcfPrimeIsOne {p} {a} pPrime pr | inr x | record { hcf = record { c = c ; c|a = c|a ; c|b = c|b ; hcf = hcf } ; extended1 = extended1 ; extended2 = extended2 ; extendedProof = extendedProof } rewrite x = exFalso (pr c|a)

reduceEquationMod : {a b c : ℕ} → (d : ℕ) → (a ∣ b) → (a ∣ c) → b ≡ c +N d → a ∣ d
reduceEquationMod {a} {b} {c} 0 a|b a|c pr = aDivZero a
reduceEquationMod {a} {b} {c} (succ d) (divides record { quot = b/a ; rem = .0 ; pr = prb/a ; remIsSmall = r1 ; quotSmall = qSm1 } refl) (divides record { quot = c/a ; rem = .0 ; pr = prc/a ; remIsSmall = r2 ; quotSmall = qSm2 } refl) b=c+d = identityOfIndiscernablesRight _∣_ a|b-c ex
  where
    c<b : c <N b
    c<b rewrite succExtracts c d | Semiring.commutative ℕSemiring c d = le d (equalityCommutative b=c+d)
    a|b-c : a ∣ subtractionNResult.result (-N (inl c<b))
    a|b-c = dividesBothImpliesDividesDifference (divides record { quot = b/a ; rem = 0 ; pr = prb/a ; remIsSmall = r1 ; quotSmall = qSm1 } refl) (divides record { quot = c/a ; rem = 0 ; pr = prc/a ; remIsSmall = r2 ; quotSmall = qSm2 } refl) c<b
    ex : subtractionNResult.result (-N {c} {b} (inl c<b)) ≡ subtractionNResult.result (-N {0} {succ d} (inl (succIsPositive d)))
    ex = equivalentSubtraction c (succ d) b 0 (c<b) (succIsPositive d) (equalityCommutative (identityOfIndiscernablesLeft _≡_ b=c+d (equalityCommutative (Semiring.sumZeroRight ℕSemiring b))))

primesArePrime : {p : ℕ} → {a b : ℕ} → (Prime p) → p ∣ (a *N b) → (p ∣ a) || (p ∣ b)
primesArePrime {p} {a} {b} pPrime pr with divisionDecidable p a
primesArePrime {p} {a} {b} pPrime pr | inl p|a = inl p|a
primesArePrime {p} {a} {b} pPrime (divides record {quot = ab/p ; rem = .0 ; pr = p|ab ; remIsSmall = _ ; quotSmall = quotSmall } refl) | inr notp|a = inr (answer ex'')
  where
    euc : extendedHcf a p
    euc = euclid a p
    h : extendedHcf.c euc ≡ 1
    h = hcfPrimeIsOne {p} {a} pPrime notp|a
    x = extendedHcf.extended1 euc
    y = extendedHcf.extended2 euc
    extended : ((a *N x) ≡ p *N y +N extendedHcf.c euc) || (a *N x +N extendedHcf.c euc ≡ p *N y)
    extended = extendedHcf.extendedProof euc
    extended' : (a *N x ≡ p *N y +N 1) || (a *N x +N 1 ≡ p *N y)
    extended' rewrite equalityCommutative h = extended
    extended'' : ((a *N x ≡ p *N y +N 1) || (a *N x +N 1 ≡ p *N y)) → (b *N (a *N x) ≡ b *N (p *N y +N 1)) || (b *N (a *N x +N 1) ≡ b *N (p *N y))
    extended'' (inl z) = inl (applyEquality (λ t → b *N t) z)
    extended'' (inr z) = inr (applyEquality (λ t → b *N t) z)
    ex : (b *N (a *N x) ≡ b *N (p *N y +N 1)) || (b *N (a *N x +N 1) ≡ b *N (p *N y)) → ((b *N a) *N x ≡ (b *N (p *N y) +N b)) || (((b *N a) *N x +N b) ≡ b *N (p *N y))
    ex (inl z) rewrite Semiring.*Associative ℕSemiring b a x | Semiring.+DistributesOver* ℕSemiring b (p *N y) 1 | Semiring.productOneRight ℕSemiring b = inl z
    ex (inr z) rewrite Semiring.+DistributesOver* ℕSemiring b (a *N x) 1 | Semiring.*Associative ℕSemiring b a x | Semiring.productOneRight ℕSemiring b = inr z
    ex' : ((a *N b) *N x ≡ ((p *N y) *N b +N b)) || (((a *N b) *N x +N b) ≡ (p *N y) *N b)
    ex' rewrite multiplicationNIsCommutative a b | multiplicationNIsCommutative (p *N y) b = ex (extended'' extended')
    ex'' : ((a *N b) *N x ≡ (p *N (y *N b) +N b)) || (((a *N b) *N x +N b) ≡ p *N (y *N b))
    ex'' rewrite Semiring.*Associative ℕSemiring (p) y b = ex'
    inter1 : p ∣ (a *N b) *N x
    inter1 = divides (record {quot = ab/p *N x ; rem = 0 ; pr = g ; remIsSmall = zeroIsValidRem p ; quotSmall = qsm quotSmall}) refl
      where
        g' : p *N ab/p ≡ a *N b
        g' rewrite Semiring.sumZeroRight ℕSemiring (p *N ab/p) = p|ab
        g'' : p *N (ab/p *N x) ≡ (a *N b) *N x
        g'' rewrite Semiring.*Associative ℕSemiring (p) ab/p x = applyEquality (λ t → t *N x) g'
        g : p *N (ab/p *N x) +N 0 ≡ (a *N b) *N x
        g rewrite Semiring.sumZeroRight ℕSemiring (p *N (ab/p *N x)) = g''
        qsm : ((0 <N p) || ((0 ≡ p) && (ab/p ≡ 0))) → (0 <N p) || ((0 ≡ p) && (ab/p *N x ≡ 0))
        qsm (inl pr) = inl pr
        qsm (inr (pr1 ,, pr2)) = inr (pr1 ,, blah)
          where
            blah : ab/p *N x ≡ 0
            blah rewrite pr2 = refl
    inter2 : ((0 <N p) || ((0 ≡ p) && (ab/p ≡ 0))) → p ∣ (p *N (y *N b))
    inter2 (inl 0<p) = divides (record {quot = y *N b ; rem = 0 ; pr = Semiring.sumZeroRight ℕSemiring (p *N (y *N b)) ; remIsSmall = zeroIsValidRem p ; quotSmall = inl 0<p }) refl
    inter2 (inr (0=p ,, ab/p=0)) = divides (record {quot = y *N b ; rem = 0 ; pr = Semiring.sumZeroRight ℕSemiring (p *N (y *N b)) ; remIsSmall = zeroIsValidRem p ; quotSmall = inr (0=p ,, blah) }) refl
      where
        oneZero : (a ≡ 0) || (b ≡ 0)
        oneZero rewrite Semiring.commutative ℕSemiring (p *N ab/p) 0 | ab/p=0 | equalityCommutative 0=p = productZeroImpliesOperandZero (equalityCommutative p|ab)
        blah : y *N b ≡ 0
        blah with oneZero
        blah | inl x1 = exFalso (notp|a p|a)
          where
            p|a : p ∣ a
            p|a rewrite x1 = aDivZero p
        blah | inr x1 rewrite x1 = Semiring.productZeroRight ℕSemiring y
    answer : ((a *N b) *N x ≡ (p *N (y *N b) +N b)) || (((a *N b) *N x +N b) ≡ p *N (y *N b)) → (p ∣ b)
    answer (inl z) = reduceEquationMod {p} b inter1 (inter2 quotSmall) z
    answer (inr z) = reduceEquationMod {p} b (inter2 quotSmall) inter1 (equalityCommutative z)

primesAreBiggerThanOne : {p : ℕ} → Prime p → (1 <N p)
primesAreBiggerThanOne {zero} record { p>1 = (le x ()) ; pr = pr }
primesAreBiggerThanOne {succ zero} pr = exFalso (oneIsNotPrime pr)
primesAreBiggerThanOne {succ (succ p)} pr = succPreservesInequality (succIsPositive p)

primesAreBiggerThanZero : {p : ℕ} → Prime p → 0 <N p
primesAreBiggerThanZero {p} pr = TotalOrder.<Transitive ℕTotalOrder (succIsPositive 0) (primesAreBiggerThanOne pr)

record notDividedByLessThan (a : ℕ) (firstPossibleDivisor : ℕ) : Set where
  field
    previousDoNotDivide : ∀ x → 1 <N x → x <N firstPossibleDivisor → x ∣ a → False

alternativePrime : {a : ℕ} → 1 <N a → notDividedByLessThan a a → Prime a
alternativePrime {a} 1<a record { previousDoNotDivide = previousDoNotDivide } = record { pr = pr ; p>1 = 1<a}
  where
    pr : {x : ℕ} → (x|a : x ∣ a) (x<a : x <N a) (0<x : zero <N x) → x ≡ 1
    pr {zero} _ _ (le x ())
    pr {succ zero} _ _ _ = refl
    pr {succ (succ x)} x|a x<a 0<x = exFalso (previousDoNotDivide (succ (succ x)) (succPreservesInequality (succIsPositive x)) x<a x|a)

divisibilityTransitive : {a b c : ℕ} → a ∣ b → b ∣ c → a ∣ c
divisibilityTransitive {a} {b} {c} (divides record { quot = b/a ; rem = .0 ; pr = prDivAB ; remIsSmall = remIsSmallAB ; quotSmall = quotSmall } refl) (divides record { quot = c/b ; rem = .0 ; pr = prDivBC ; remIsSmall = remIsSmallBC } refl) = divides record { quot = b/a *N c/b ; rem = 0 ; pr = p ; remIsSmall = zeroIsValidRem a ; quotSmall = qsm quotSmall } refl
  where
    p : a *N (b/a *N c/b) +N 0 ≡ c
    p rewrite Semiring.sumZeroRight ℕSemiring (a *N (b/a *N c/b)) | Semiring.sumZeroRight ℕSemiring (b *N c/b) | Semiring.sumZeroRight ℕSemiring (a *N b/a) | Semiring.*Associative ℕSemiring a b/a c/b | prDivAB | prDivBC = refl
    qsm : ((0 <N a) || (0 ≡ a) && (b/a ≡ 0)) → ((0 <N a) || (0 ≡ a) && (b/a *N c/b ≡ 0))
    qsm (inl x) = inl x
    qsm (inr (p1 ,, p2)) = inr (p1 ,, blah)
      where
        blah : b/a *N c/b ≡ 0
        blah rewrite p2 = refl

compositeOrPrimeLemma : {a b : ℕ} → notDividedByLessThan b a → a ∣ b → {i : ℕ} → (i ∣ a) → (i <N a) → (0 <N i) → i ≡ 1
compositeOrPrimeLemma {a} {b} record { previousDoNotDivide = previousDoNotDivide } a|b {zero} i|a i<a 0<i = exFalso (lessIrreflexive 0<i)
compositeOrPrimeLemma {a} {b} record { previousDoNotDivide = previousDoNotDivide } a|b {succ zero} i|a i<a 0<i = refl
compositeOrPrimeLemma {a} {b} record { previousDoNotDivide = previousDoNotDivide } a|b {succ (succ i)} i|a i<a 0<i = exFalso (previousDoNotDivide (succ (succ i)) (succPreservesInequality (succIsPositive i)) i<a (divisibilityTransitive i|a a|b) )

compositeOrPrime : (a : ℕ) → (1 <N a) → (Composite a) || (Prime a)
compositeOrPrime a pr = go''' go''
  where
    base : notDividedByLessThan a 2
    base = record { previousDoNotDivide = λ x 1<x x<2 _ → noIntegersBetweenXAndSuccX 1 1<x x<2 }
    go : {firstPoss : ℕ} → notDividedByLessThan a firstPoss → ((notDividedByLessThan a (succ firstPoss)) || ((firstPoss ∣ a) && (firstPoss <N a))) || (firstPoss ≡ a)
    go' : (firstPoss : ℕ) → (((notDividedByLessThan a firstPoss) || (Composite a))) || (notDividedByLessThan a a)
    go'' : (notDividedByLessThan a a) || (Composite a)
    go'' with go' a
    ... | inr x = inl x
    ... | inl x = x
    go''' : ((notDividedByLessThan a a) || (Composite a)) → ((Composite a) || (Prime a))
    go''' (inl x) = inr (alternativePrime pr x)
    go''' (inr x) = inl x
    go' (zero) = inl (inl (record { previousDoNotDivide = λ x 1<x x<0 _ → zeroNeverGreater x<0 }))
    go' (succ 0) = inl (inl (record { previousDoNotDivide = λ x 1<x x<1 _ → TotalOrder.irreflexive ℕTotalOrder (TotalOrder.<Transitive ℕTotalOrder x<1 1<x) }))
    go' (succ (succ zero)) = inl (inl base)
    go' (succ (succ (succ firstPoss))) with go' (succ (succ firstPoss))
    go' (succ (succ (succ firstPoss))) | inl (inl x) with go {succ (succ firstPoss)} x
    go' (succ (succ (succ firstPoss))) | inl (inl x) | inl (inl x1) = inl (inl x1)
    go' (succ (succ (succ firstPoss))) | inl (inl x) | inl (inr x1) = inl (inr record { noSmallerDivisors = λ i i<ssFP 1<i i|a → notDividedByLessThan.previousDoNotDivide x i 1<i i<ssFP i|a ; n>1 = pr ; divisor = succ (succ firstPoss) ; dividesN = _&&_.fst x1 ; divisorLessN = _&&_.snd x1 ; divisorNot1 = succPreservesInequality (succIsPositive firstPoss) ; divisorPrime = record { p>1 = succPreservesInequality (succIsPositive firstPoss) ; pr = compositeOrPrimeLemma {succ (succ firstPoss)} {a} x (_&&_.fst x1) } })
    go' (succ (succ (succ firstPoss))) | inl (inl x) | inr y rewrite y = inr x
    go' (succ (succ (succ firstPoss))) | inl (inr x) = inl (inr x)
    go' (succ (succ (succ firstPoss))) | inr x = inr x

    go {zero} pr = inl (inl (record { previousDoNotDivide = λ x 1<x x<1 _ → irreflexive (<Transitive x<1 1<x)}))
    go {succ firstPoss} knownCoprime with totality (succ firstPoss) a
    go {succ firstPoss} knownCoprime | inr x = inr x
    go {succ firstPoss} knownCoprime | inl (inl sFP<a) with divisionAlg (succ firstPoss) a
    go {succ firstPoss} knownCoprime | inl (inl sFP<a) | record { quot = quot ; rem = zero ; pr = pr ; remIsSmall = remIsSmall } = inl (inr record { fst = (divides (record { quot = quot ; rem = zero ; remIsSmall = remIsSmall ; pr = pr ; quotSmall = inl (succIsPositive firstPoss) }) refl) ; snd = sFP<a })
    go {succ firstPoss} knownCoprime | inl (inl sFP<a) | record { quot = quot ; rem = succ rem ; pr = pr ; remIsSmall = remIsSmall } = inl next
      where
        previous : ∀ x → 1 <N x → x <N succ firstPoss → x ∣ a → False
        previous = notDividedByLessThan.previousDoNotDivide knownCoprime
        next : notDividedByLessThan a (succ (succ firstPoss)) || (((succ firstPoss) ∣ a) && (succ firstPoss <N a))
        next with divisionAlg (succ firstPoss) a
        next | record { quot = quot ; rem = zero ; pr = pr ; remIsSmall = remIsSmall } = inr (record { fst = divides record { quot = quot ; rem = zero ; pr = pr ; remIsSmall = remIsSmall ; quotSmall = inl (succIsPositive firstPoss) } refl ; snd = sFP<a } )
        next | record { quot = quot ; rem = succ rem ; pr = pr ; remIsSmall = remIsSmall } = inl record { previousDoNotDivide = (next' record { quot = quot ; rem = succ rem ; pr = pr ; remIsSmall = remIsSmall ; quotSmall = inl (succIsPositive firstPoss)  } (succIsPositive rem)) }
          where
            next' : (res : divisionAlgResult (succ firstPoss) a) → (pr : 0 <N divisionAlgResult.rem res) → (x : ℕ) → 1 <N x → x <N succ (succ firstPoss) → x ∣ a → False
            next' (res) (prDiv) x 1<x x<ssFirstposs x|a with totality x (succ firstPoss)
            next' (res) (prDiv) x 1<x x<ssFirstposs x|a | inl (inl x<sFirstPoss) = previous x 1<x x<sFirstPoss x|a
            next' (res) (prDiv) x 1<x x<ssFirstposs x|a | inl (inr sFirstPoss<x) = noIntegersBetweenXAndSuccX (succ firstPoss) sFirstPoss<x x<ssFirstposs
            next' res prDiv x 1<x x<ssFirstposs (divides res1 x1) | inr x=sFirstPoss rewrite equalityCommutative x=sFirstPoss = g
              where
                g : False
                g with modIsUnique res res1
                ... | r rewrite r = lessImpliesNotEqual prDiv (equalityCommutative x1)
    go {succ firstPoss} record { previousDoNotDivide = previousDoNotDivide } | inl (inr a<sFP) = exFalso (previousDoNotDivide a pr a<sFP (aDivA a))

primeDivPrimeImpliesEqual : {p1 p2 : ℕ} → Prime p1 → Prime p2 → p1 ∣ p2 → p1 ≡ p2
primeDivPrimeImpliesEqual {p1} {p2} pr1 pr2 p1|p2 with totality p1 p2
primeDivPrimeImpliesEqual {p1} {p2} pr1 record { p>1 = p>1 ; pr = pr } p1|p2 | inl (inl p1<p2) with pr p1|p2 p1<p2 (primesAreBiggerThanZero {p1} pr1)
... | p1=1 = exFalso (oneIsNotPrime contr)
  where
    contr : Prime 1
    contr rewrite p1=1 = pr1
primeDivPrimeImpliesEqual {p1} {zero} pr1 pr2 p1|p2 | inl (inr p1>p2) = exFalso (zeroIsNotPrime pr2)
primeDivPrimeImpliesEqual {p1} {succ p2} pr1 pr2 p1|p2 | inl (inr p1>p2) = exFalso (divisorIsSmaller p1|p2 p1>p2)
primeDivPrimeImpliesEqual {p1} {p2} pr1 pr2 p1|p2 | inr p1=p2 = p1=p2

mult1Lemma : {a b : ℕ} → a *N succ b ≡ 1 → (a ≡ 1) && (b ≡ 0)
mult1Lemma {a} {b} pr = record { fst = _&&_.fst p ; snd = q}
  where
    p : (a ≡ 1) && (succ b ≡ 1)
    p = productOneImpliesOperandsOne pr
    q : b ≡ zero
    q = succInjective (_&&_.snd p)

oneHasNoDivisors : {a : ℕ} → a ∣ 1 → a ≡ 1
oneHasNoDivisors {a} (divides record { quot = zero ; rem = .0 ; pr = pr ; remIsSmall = remIsSmall } refl) rewrite Semiring.sumZeroRight ℕSemiring (a *N zero) | multiplicationNIsCommutative a zero | Semiring.sumZeroRight ℕSemiring a = exFalso (naughtE pr)
oneHasNoDivisors {a} (divides record { quot = (succ quot) ; rem = .0 ; pr = pr ; remIsSmall = remIsSmall } refl) rewrite Semiring.sumZeroRight ℕSemiring (a *N succ quot) = _&&_.fst (mult1Lemma pr)

notSmallerMeansGE : {a b : ℕ} → (a <N b → False) → b ≤N a
notSmallerMeansGE {a} {b} notA<b with totality a b
notSmallerMeansGE {a} {b} notA<b | inl (inl x) = exFalso (notA<b x)
notSmallerMeansGE {a} {b} notA<b | inl (inr x) = inl x
notSmallerMeansGE {a} {b} notA<b | inr x = inr (equalityCommutative x)