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

open import LogicalFormulae
open import Lists.Lists
open import Numbers.Naturals.Order
open import Numbers.Naturals.Order.Lemmas
open import Numbers.Naturals.Semiring
open import Numbers.BinaryNaturals.Definition
open import Orders.Total.Definition
open import Semirings.Definition

module Numbers.BinaryNaturals.Order where

data Compare : Set where
  Equal : Compare
  FirstLess : Compare
  FirstGreater : Compare

private
  badCompare : Equal ≡ FirstLess → False
  badCompare ()

  badCompare' : Equal ≡ FirstGreater → False
  badCompare' ()

  badCompare'' : FirstLess ≡ FirstGreater → False
  badCompare'' ()

_<BInherited_ : BinNat → BinNat → Compare
a <BInherited b with TotalOrder.totality ℕTotalOrder (binNatToN a) (binNatToN b)
(a <BInherited b) | inl (inl x) = FirstLess
(a <BInherited b) | inl (inr x) = FirstGreater
(a <BInherited b) | inr x = Equal

private
  go<B : Compare → BinNat → BinNat → Compare
  go<B Equal [] [] = Equal
  go<B Equal [] (zero :: b) = go<B Equal [] b
  go<B Equal [] (one :: b) = FirstLess
  go<B Equal (zero :: a) [] = go<B Equal a []
  go<B Equal (zero :: a) (zero :: b) = go<B Equal a b
  go<B Equal (zero :: a) (one :: b) = go<B FirstLess a b
  go<B Equal (one :: a) [] = FirstGreater
  go<B Equal (one :: a) (zero :: b) = go<B FirstGreater a b
  go<B Equal (one :: a) (one :: b) = go<B Equal a b
  go<B FirstGreater [] [] = FirstGreater
  go<B FirstGreater [] (zero :: b) = go<B FirstGreater [] b
  go<B FirstGreater [] (one :: b) = FirstLess
  go<B FirstGreater (zero :: a) [] = FirstGreater
  go<B FirstGreater (zero :: a) (zero :: b) = go<B FirstGreater a b
  go<B FirstGreater (zero :: a) (one :: b) = go<B FirstLess a b
  go<B FirstGreater (one :: a) [] = FirstGreater
  go<B FirstGreater (one :: a) (zero :: b) = go<B FirstGreater a b
  go<B FirstGreater (one :: a) (one :: b) = go<B FirstGreater a b
  go<B FirstLess [] b = FirstLess
  go<B FirstLess (zero :: a) [] = go<B FirstLess a []
  go<B FirstLess (one :: a) [] = FirstGreater
  go<B FirstLess (zero :: a) (zero :: b) = go<B FirstLess a b
  go<B FirstLess (zero :: a) (one :: b) = go<B FirstLess a b
  go<B FirstLess (one :: a) (zero :: b) = go<B FirstGreater a b
  go<B FirstLess (one :: a) (one :: b) = go<B FirstLess a b

_<B_ : BinNat → BinNat → Compare
a <B b = go<B Equal a b

private
  lemma1 : {s : Compare} → (n : BinNat) → go<B s n n ≡ s
  lemma1 {Equal} [] = refl
  lemma1 {Equal} (zero :: n) = lemma1 n
  lemma1 {Equal} (one :: n) = lemma1 n
  lemma1 {FirstLess} [] = refl
  lemma1 {FirstLess} (zero :: n) = lemma1 n
  lemma1 {FirstLess} (one :: n) = lemma1 n
  lemma1 {FirstGreater} [] = refl
  lemma1 {FirstGreater} (zero :: n) = lemma1 n
  lemma1 {FirstGreater} (one :: n) = lemma1 n

  lemma : {s : Compare} → (n : BinNat) → go<B s (incr n) n ≡ FirstGreater
  lemma {Equal} [] = refl
  lemma {Equal} (zero :: n) = lemma1 n
  lemma {Equal} (one :: n) = lemma {FirstLess} n
  lemma {FirstLess} [] = refl
  lemma {FirstLess} (zero :: n) = lemma1 n
  lemma {FirstLess} (one :: n) = lemma {FirstLess} n
  lemma {FirstGreater} [] = refl
  lemma {FirstGreater} (zero :: n) = lemma1 {FirstGreater} n
  lemma {FirstGreater} (one :: n) = lemma {FirstLess} n

  succLess : (n : ℕ) → (NToBinNat (succ n)) <B (NToBinNat n) ≡ FirstGreater
  succLess zero = refl
  succLess (succ n) with NToBinNat n
  succLess (succ n) | [] = refl
  succLess (succ n) | zero :: bl = lemma {FirstLess} bl
  succLess (succ n) | one :: bl = lemma1 {FirstGreater} (incr bl)

  compareRefl : (n : BinNat) → n <B n ≡ Equal
  compareRefl [] = refl
  compareRefl (zero :: n) = compareRefl n
  compareRefl (one :: n) = compareRefl n

  zeroLess : (n : BinNat) → ((canonical n ≡ []) → False) → [] <B n ≡ FirstLess
  zeroLess [] pr = exFalso (pr refl)
  zeroLess (zero :: n) pr with inspect (canonical n)
  zeroLess (zero :: n) pr | [] with≡ x rewrite x = exFalso (pr refl)
  zeroLess (zero :: n) pr | (x₁ :: y) with≡ x = zeroLess n λ i → nonEmptyNotEmpty (transitivity (equalityCommutative x) i)
  zeroLess (one :: n) pr = refl

  zeroLess' : (n : BinNat) → ((canonical n ≡ []) → False) → n <B [] ≡ FirstGreater
  zeroLess' [] pr = exFalso (pr refl)
  zeroLess' (zero :: n) pr with inspect (canonical n)
  zeroLess' (zero :: n) pr | [] with≡ x rewrite x = exFalso (pr refl)
  zeroLess' (zero :: n) pr | (x₁ :: y) with≡ x = zeroLess' n (λ i → nonEmptyNotEmpty (transitivity (equalityCommutative x) i))
  zeroLess' (one :: n) pr = refl

  canonicalFirst : (n m : BinNat) (state : Compare) → go<B state n m ≡ go<B state (canonical n) m
  canonicalFirst [] m Equal = refl
  canonicalFirst (zero :: n) m Equal with inspect (canonical n)
  canonicalFirst (zero :: n) [] Equal | [] with≡ x rewrite x = transitivity (canonicalFirst n [] Equal) (applyEquality (λ i → go<B Equal i []) {canonical n} x)
  canonicalFirst (zero :: n) (zero :: ms) Equal | [] with≡ x rewrite x | canonicalFirst n ms Equal | x = refl
  canonicalFirst (zero :: n) (one :: ms) Equal | [] with≡ x rewrite x | canonicalFirst n ms FirstLess | x = refl
  canonicalFirst (zero :: n) [] Equal | (x₁ :: y) with≡ x rewrite x | canonicalFirst n [] Equal | x = refl
  canonicalFirst (zero :: n) (zero :: ms) Equal | (x₁ :: y) with≡ x rewrite x | canonicalFirst n ms Equal | x = refl
  canonicalFirst (zero :: n) (one :: ms) Equal | (x₁ :: y) with≡ x rewrite x | canonicalFirst n ms FirstLess | x = refl
  canonicalFirst (one :: n) [] Equal = refl
  canonicalFirst (one :: n) (zero :: m) Equal = canonicalFirst n m FirstGreater
  canonicalFirst (one :: n) (one :: m) Equal = canonicalFirst n m Equal
  canonicalFirst [] m FirstLess = refl
  canonicalFirst (zero :: n) [] FirstLess with inspect (canonical n)
  canonicalFirst (zero :: n) [] FirstLess | [] with≡ x rewrite x | canonicalFirst n [] FirstLess | x = refl
  canonicalFirst (zero :: n) [] FirstLess | (x₁ :: y) with≡ x rewrite x | canonicalFirst n [] FirstLess | x = refl
  canonicalFirst (zero :: n) (zero :: m) FirstLess with inspect (canonical n)
  canonicalFirst (zero :: n) (zero :: m) FirstLess | [] with≡ x rewrite x | canonicalFirst n m FirstLess | x = refl
  canonicalFirst (zero :: n) (zero :: m) FirstLess | (x₁ :: y) with≡ x rewrite x | canonicalFirst n m FirstLess | x = refl
  canonicalFirst (zero :: n) (one :: m) FirstLess with inspect (canonical n)
  canonicalFirst (zero :: n) (one :: m) FirstLess | [] with≡ x rewrite x | canonicalFirst n m FirstLess | x = refl
  canonicalFirst (zero :: n) (one :: m) FirstLess | (x₁ :: y) with≡ x rewrite x | canonicalFirst n m FirstLess | x = refl
  canonicalFirst (one :: n) [] FirstLess = refl
  canonicalFirst (one :: n) (zero :: m) FirstLess = canonicalFirst n m FirstGreater
  canonicalFirst (one :: n) (one :: m) FirstLess = canonicalFirst n m FirstLess
  canonicalFirst [] m FirstGreater = refl
  canonicalFirst (zero :: n) m FirstGreater with inspect (canonical n)
  canonicalFirst (zero :: n) [] FirstGreater | [] with≡ x rewrite x = refl
  canonicalFirst (zero :: n) (zero :: ms) FirstGreater | [] with≡ x rewrite x | canonicalFirst n ms FirstGreater | x = refl
  canonicalFirst (zero :: n) (one :: ms) FirstGreater | [] with≡ x rewrite x | canonicalFirst n ms FirstLess | x = refl
  canonicalFirst (zero :: n) [] FirstGreater | (x₁ :: y) with≡ x rewrite x = refl
  canonicalFirst (zero :: n) (zero :: ms) FirstGreater | (x₁ :: y) with≡ x rewrite x | canonicalFirst n ms FirstGreater | x = refl
  canonicalFirst (zero :: n) (one :: ms) FirstGreater | (x₁ :: y) with≡ x rewrite x | canonicalFirst n ms FirstLess | x = refl
  canonicalFirst (one :: n) [] FirstGreater = refl
  canonicalFirst (one :: n) (zero :: m) FirstGreater = canonicalFirst n m FirstGreater
  canonicalFirst (one :: n) (one :: m) FirstGreater = canonicalFirst n m FirstGreater

  greater0Lemma : (n : BinNat) → go<B FirstGreater n [] ≡ FirstGreater
  greater0Lemma [] = refl
  greater0Lemma (zero :: n) = refl
  greater0Lemma (one :: n) = refl

  canonicalSecond : (n m : BinNat) (state : Compare) → go<B state n m ≡ go<B state n (canonical m)
  canonicalSecond n [] Equal = refl
  canonicalSecond [] (zero :: m) Equal with inspect (canonical m)
  canonicalSecond [] (zero :: m) Equal | [] with≡ x rewrite x | canonicalSecond [] m Equal | x = refl
  canonicalSecond [] (zero :: m) Equal | (x₁ :: y) with≡ x rewrite x | canonicalSecond [] m Equal | x = refl
  canonicalSecond (zero :: n) (zero :: m) Equal with inspect (canonical m)
  canonicalSecond (zero :: n) (zero :: m) Equal | [] with≡ x rewrite x | canonicalSecond n m Equal | x = refl
  canonicalSecond (zero :: n) (zero :: m) Equal | (x₁ :: y) with≡ x rewrite x | canonicalSecond n m Equal | x = refl
  canonicalSecond (one :: n) (zero :: m) Equal with inspect (canonical m)
  canonicalSecond (one :: n) (zero :: m) Equal | [] with≡ x rewrite x | canonicalSecond n m FirstGreater | x = greater0Lemma n
  canonicalSecond (one :: n) (zero :: m) Equal | (x₁ :: y) with≡ x rewrite x | canonicalSecond n m FirstGreater | x = refl
  canonicalSecond [] (one :: m) Equal = refl
  canonicalSecond (zero :: n) (one :: m) Equal = canonicalSecond n m FirstLess
  canonicalSecond (one :: n) (one :: m) Equal = canonicalSecond n m Equal
  canonicalSecond n [] FirstLess = refl
  canonicalSecond [] (zero :: m) FirstLess = refl
  canonicalSecond (x :: n) (zero :: m) FirstLess with inspect (canonical m)
  canonicalSecond (zero :: n) (zero :: m) FirstLess | [] with≡ x rewrite x | canonicalSecond n m FirstLess | x = refl
  canonicalSecond (one :: n) (zero :: m) FirstLess | [] with≡ x rewrite x | canonicalSecond n m FirstGreater | x = greater0Lemma n
  canonicalSecond (zero :: n) (zero :: m) FirstLess | (x₁ :: bl) with≡ pr rewrite pr | canonicalSecond n m FirstLess | pr = refl
  canonicalSecond (one :: n) (zero :: m) FirstLess | (x₁ :: bl) with≡ pr rewrite pr | canonicalSecond n m FirstGreater | pr = refl
  canonicalSecond [] (one :: m) FirstLess = refl
  canonicalSecond (zero :: n) (one :: m) FirstLess = canonicalSecond n m FirstLess
  canonicalSecond (one :: n) (one :: m) FirstLess = canonicalSecond n m FirstLess
  canonicalSecond n [] FirstGreater = refl
  canonicalSecond [] (zero :: m) FirstGreater with inspect (canonical m)
  canonicalSecond [] (zero :: m) FirstGreater | [] with≡ x rewrite x | canonicalSecond [] m FirstGreater | x = refl
  canonicalSecond [] (zero :: m) FirstGreater | (x₁ :: y) with≡ x rewrite x | canonicalSecond [] m FirstGreater | x = refl
  canonicalSecond (zero :: n) (zero :: m) FirstGreater with inspect (canonical m)
  canonicalSecond (zero :: n) (zero :: m) FirstGreater | [] with≡ x rewrite x | canonicalSecond n m FirstGreater | x = greater0Lemma n
  canonicalSecond (zero :: n) (zero :: m) FirstGreater | (x₁ :: y) with≡ x rewrite x | canonicalSecond n m FirstGreater | x = refl
  canonicalSecond (one :: n) (zero :: m) FirstGreater with inspect (canonical m)
  canonicalSecond (one :: n) (zero :: m) FirstGreater | [] with≡ x rewrite x | canonicalSecond n m FirstGreater | x = greater0Lemma n
  canonicalSecond (one :: n) (zero :: m) FirstGreater | (x₁ :: y) with≡ x rewrite x | canonicalSecond n m FirstGreater | x = refl
  canonicalSecond [] (one :: m) FirstGreater = refl
  canonicalSecond (zero :: n) (one :: m) FirstGreater = canonicalSecond n m FirstLess
  canonicalSecond (one :: n) (one :: m) FirstGreater = canonicalSecond n m FirstGreater

  equalContaminated : (n m : BinNat) → go<B FirstLess n m ≡ Equal → False
  equalContaminated' : (n m : BinNat) → go<B FirstGreater n m ≡ Equal → False

  equalContaminated (zero :: n) [] pr = equalContaminated n [] pr
  equalContaminated (zero :: n) (zero :: m) pr = equalContaminated n m pr
  equalContaminated (zero :: n) (one :: m) pr = equalContaminated n m pr
  equalContaminated (one :: n) (zero :: m) pr = equalContaminated' n m pr
  equalContaminated (one :: n) (one :: m) pr = equalContaminated n m pr

  equalContaminated' [] (zero :: m) pr = equalContaminated' [] m pr
  equalContaminated' (zero :: n) (zero :: m) pr = equalContaminated' n m pr
  equalContaminated' (zero :: n) (one :: m) pr = equalContaminated n m pr
  equalContaminated' (one :: n) (zero :: m) pr = equalContaminated' n m pr
  equalContaminated' (one :: n) (one :: m) pr = equalContaminated' n m pr

  comparisonEqual : (a b : BinNat) → (a <B b ≡ Equal) → canonical a ≡ canonical b
  comparisonEqual [] [] pr = refl
  comparisonEqual [] (zero :: b) pr with inspect (canonical b)
  comparisonEqual [] (zero :: b) pr | [] with≡ p rewrite p = refl
  comparisonEqual [] (zero :: b) pr | (x :: r) with≡ p rewrite zeroLess b (λ i → nonEmptyNotEmpty (transitivity (equalityCommutative p) i)) = exFalso (badCompare (equalityCommutative pr))
  comparisonEqual (zero :: a) [] pr with inspect (canonical a)
  comparisonEqual (zero :: a) [] pr | [] with≡ x rewrite x = refl
  comparisonEqual (zero :: a) [] pr | (x₁ :: y) with≡ x rewrite zeroLess' a (λ i → nonEmptyNotEmpty (transitivity (equalityCommutative x) i)) = exFalso (badCompare' (equalityCommutative pr))
  comparisonEqual (zero :: a) (zero :: b) pr with inspect (canonical a)
  comparisonEqual (zero :: a) (zero :: b) pr | [] with≡ x with inspect (canonical b)
  comparisonEqual (zero :: a) (zero :: b) pr | [] with≡ pr2 | [] with≡ pr3 rewrite pr2 | pr3 = refl
  comparisonEqual (zero :: a) (zero :: b) pr | [] with≡ pr2 | (x₂ :: y) with≡ pr3 rewrite pr2 | pr3 | comparisonEqual a b pr = exFalso (nonEmptyNotEmpty (transitivity (equalityCommutative pr3) pr2))
  comparisonEqual (zero :: a) (zero :: b) pr | (c :: cs) with≡ pr2 with inspect (canonical b)
  comparisonEqual (zero :: a) (zero :: b) pr | (c :: cs) with≡ pr2 | [] with≡ pr3 rewrite pr2 | pr3 | comparisonEqual a b pr = exFalso (nonEmptyNotEmpty (transitivity (equalityCommutative pr2) pr3))
  comparisonEqual (zero :: a) (zero :: b) pr | (c :: cs) with≡ pr2 | (x₁ :: y) with≡ pr3 rewrite pr2 | pr3 | comparisonEqual a b pr = applyEquality (zero ::_) (transitivity (equalityCommutative pr2) pr3)
  comparisonEqual (zero :: a) (one :: b) pr = exFalso (equalContaminated a b pr)
  comparisonEqual (one :: a) (zero :: b) pr = exFalso (equalContaminated' a b pr)
  comparisonEqual (one :: a) (one :: b) pr = applyEquality (one ::_) (comparisonEqual a b pr)

  equalSymmetric : (n m : BinNat) → n <B m ≡ Equal → m <B n ≡ Equal
  equalSymmetric [] [] n=m = refl
  equalSymmetric [] (zero :: m) n=m rewrite equalSymmetric [] m n=m = refl
  equalSymmetric (zero :: n) [] n=m rewrite equalSymmetric n [] n=m = refl
  equalSymmetric (zero :: n) (zero :: m) n=m = equalSymmetric n m n=m
  equalSymmetric (zero :: n) (one :: m) n=m = exFalso (equalContaminated n m n=m)
  equalSymmetric (one :: n) (zero :: m) n=m = exFalso (equalContaminated' n m n=m)
  equalSymmetric (one :: n) (one :: m) n=m = equalSymmetric n m n=m

  equalToFirstGreater : (state : Compare) → (a b : BinNat) → go<B Equal a b ≡ FirstGreater → go<B state a b ≡ FirstGreater
  equalToFirstGreater FirstGreater [] (zero :: b) pr = equalToFirstGreater FirstGreater [] b pr
  equalToFirstGreater FirstGreater (zero :: a) [] pr = refl
  equalToFirstGreater FirstGreater (zero :: a) (zero :: b) pr = equalToFirstGreater FirstGreater a b pr
  equalToFirstGreater FirstGreater (zero :: a) (one :: b) pr = pr
  equalToFirstGreater FirstGreater (one :: a) [] pr = refl
  equalToFirstGreater FirstGreater (one :: a) (zero :: b) pr = pr
  equalToFirstGreater FirstGreater (one :: a) (one :: b) pr = equalToFirstGreater FirstGreater a b pr
  equalToFirstGreater Equal a b pr = pr
  equalToFirstGreater FirstLess [] (zero :: b) pr = equalToFirstGreater FirstLess [] b pr
  equalToFirstGreater FirstLess (zero :: a) [] pr = equalToFirstGreater FirstLess a [] pr
  equalToFirstGreater FirstLess (zero :: a) (zero :: b) pr = equalToFirstGreater FirstLess a b pr
  equalToFirstGreater FirstLess (zero :: a) (one :: b) pr = pr
  equalToFirstGreater FirstLess (one :: a) [] pr = refl
  equalToFirstGreater FirstLess (one :: a) (zero :: b) pr = pr
  equalToFirstGreater FirstLess (one :: a) (one :: b) pr = equalToFirstGreater FirstLess a b pr

  equalToFirstLess : (state : Compare) → (a b : BinNat) → go<B Equal a b ≡ FirstLess → go<B state a b ≡ FirstLess
  equalToFirstLess FirstLess [] b pr = refl
  equalToFirstLess FirstLess (zero :: a) [] pr = equalToFirstLess FirstLess a [] pr
  equalToFirstLess FirstLess (zero :: a) (zero :: b) pr = equalToFirstLess FirstLess a b pr
  equalToFirstLess FirstLess (zero :: a) (one :: b) pr = pr
  equalToFirstLess FirstLess (one :: a) (zero :: b) pr = pr
  equalToFirstLess FirstLess (one :: a) (one :: b) pr = equalToFirstLess FirstLess a b pr
  equalToFirstLess Equal a b pr = pr
  equalToFirstLess FirstGreater [] (zero :: b) pr = equalToFirstLess FirstGreater [] b pr
  equalToFirstLess FirstGreater [] (one :: b) pr = refl
  equalToFirstLess FirstGreater (zero :: a) [] pr = transitivity (t a) (equalToFirstLess FirstGreater a [] pr)
    where
      t : (a : BinNat) → FirstGreater ≡ go<B FirstGreater a []
      t [] = refl
      t (zero :: a) = refl
      t (one :: a) = refl
  equalToFirstLess FirstGreater (zero :: a) (zero :: b) pr = equalToFirstLess FirstGreater a b pr
  equalToFirstLess FirstGreater (zero :: a) (one :: b) pr = pr
  equalToFirstLess FirstGreater (one :: a) (zero :: b) pr = pr
  equalToFirstLess FirstGreater (one :: a) (one :: b) pr = equalToFirstLess FirstGreater a b pr

  zeroNotSucc : (n : ℕ) (b : BinNat) → (canonical b ≡ []) → (binNatToN b ≡ succ n) → False
  zeroNotSucc n b b=0 b>0 rewrite binNatToNZero' b b=0 = naughtE b>0

  chopFirstBit : (m n : BinNat) {b : Bit} (s : Compare) → go<B s (b :: m) (b :: n) ≡ go<B s m n
  chopFirstBit m n {zero} Equal = refl
  chopFirstBit m n {one} Equal = refl
  chopFirstBit m n {zero} FirstLess = refl
  chopFirstBit m n {one} FirstLess = refl
  chopFirstBit m n {zero} FirstGreater = refl
  chopFirstBit m n {one} FirstGreater = refl

  chopDouble : (a b : BinNat) (i : Bit) → (i :: a) <BInherited (i :: b) ≡ a <BInherited b
  chopDouble a b i with TotalOrder.totality ℕTotalOrder (binNatToN a) (binNatToN b)
  chopDouble a b zero | inl (inl a<b) with TotalOrder.totality ℕTotalOrder (2 *N binNatToN a) (2 *N binNatToN b)
  chopDouble a b zero | inl (inl a<b) | inl (inl x) = refl
  chopDouble a b zero | inl (inl a<b) | inl (inr b<a) = exFalso (TotalOrder.irreflexive ℕTotalOrder (TotalOrder.<Transitive ℕTotalOrder b<a (lessRespectsMultiplicationLeft (binNatToN a) (binNatToN b) 2 a<b (le 1 refl))))
  chopDouble a b zero | inl (inl a<b) | inr a=b rewrite productCancelsLeft 2 (binNatToN a) (binNatToN b) (le 1 refl) a=b = exFalso (TotalOrder.irreflexive ℕTotalOrder a<b)
  chopDouble a b one | inl (inl a<b) with TotalOrder.totality ℕTotalOrder (2 *N binNatToN a) (2 *N binNatToN b)
  chopDouble a b one | inl (inl a<b) | inl (inl 2a<2b) = refl
  chopDouble a b one | inl (inl a<b) | inl (inr 2b<2a) = exFalso (TotalOrder.irreflexive ℕTotalOrder (TotalOrder.<Transitive (ℕTotalOrder) a<b (cancelInequalityLeft {2} 2b<2a)))
  chopDouble a b one | inl (inl a<b) | inr 2a=2b rewrite productCancelsLeft 2 (binNatToN a) (binNatToN b) (le 1 refl) 2a=2b = exFalso (TotalOrder.irreflexive (ℕTotalOrder) a<b)
  chopDouble a b zero | inl (inr b<a) with TotalOrder.totality ℕTotalOrder (2 *N binNatToN a) (2 *N binNatToN b)
  chopDouble a b zero | inl (inr b<a) | inl (inl 2a<2b) = exFalso (TotalOrder.irreflexive (ℕTotalOrder) (TotalOrder.<Transitive (ℕTotalOrder) b<a (cancelInequalityLeft {2} {binNatToN a} {binNatToN b} 2a<2b)))
  chopDouble a b zero | inl (inr b<a) | inl (inr 2b<2a) = refl
  chopDouble a b zero | inl (inr b<a) | inr 2a=2b rewrite productCancelsLeft 2 (binNatToN a) (binNatToN b) (le 1 refl) 2a=2b = exFalso (TotalOrder.irreflexive (ℕTotalOrder) b<a)
  chopDouble a b one | inl (inr b<a) with TotalOrder.totality ℕTotalOrder (2 *N binNatToN a) (2 *N binNatToN b)
  chopDouble a b one | inl (inr b<a) | inl (inl 2a<2b) = exFalso (TotalOrder.irreflexive (ℕTotalOrder) (TotalOrder.<Transitive (ℕTotalOrder) b<a (cancelInequalityLeft {2} 2a<2b)))
  chopDouble a b one | inl (inr b<a) | inl (inr x) = refl
  chopDouble a b one | inl (inr b<a) | inr 2a=2b rewrite productCancelsLeft 2 (binNatToN a) (binNatToN b) (le 1 refl) 2a=2b = exFalso (TotalOrder.irreflexive (ℕTotalOrder) b<a)
  chopDouble a b i | inr x with TotalOrder.totality ℕTotalOrder (binNatToN (i :: a)) (binNatToN (i :: b))
  chopDouble a b zero | inr a=b | inl (inl a<b) rewrite a=b = exFalso (TotalOrder.irreflexive (ℕTotalOrder) a<b)
  chopDouble a b one | inr a=b | inl (inl a<b) rewrite a=b = exFalso (TotalOrder.irreflexive (ℕTotalOrder) a<b)
  chopDouble a b zero | inr a=b | inl (inr b<a) rewrite a=b = exFalso (TotalOrder.irreflexive (ℕTotalOrder) b<a)
  chopDouble a b one | inr a=b | inl (inr b<a) rewrite a=b = exFalso (TotalOrder.irreflexive (ℕTotalOrder) b<a)
  chopDouble a b _ | inr a=b | inr x = refl

  succNotLess : {n : ℕ} → succ n <N n → False
  succNotLess {succ n} (le x proof) = succNotLess {n} (le x (succInjective (transitivity (applyEquality succ (transitivity (Semiring.commutative ℕSemiring (succ x) (succ n)) (transitivity (applyEquality succ (transitivity (Semiring.commutative ℕSemiring n (succ x)) (applyEquality succ (Semiring.commutative ℕSemiring x n)))) (Semiring.commutative ℕSemiring (succ (succ n)) x)))) proof)))

<BIsInherited : (a b : BinNat) → a <BInherited b ≡ a <B b
<BIsInherited [] b with TotalOrder.totality ℕTotalOrder 0 (binNatToN b)
<BIsInherited [] b | inl (inl x) with inspect (binNatToN b)
<BIsInherited [] b | inl (inl x) | 0 with≡ pr rewrite binNatToNZero b pr | pr = exFalso (TotalOrder.irreflexive (ℕTotalOrder) x)
<BIsInherited [] b | inl (inl x) | (succ bl) with≡ pr rewrite pr = equalityCommutative (zeroLess b λ p → zeroNotSucc bl b p pr)
<BIsInherited [] b | inr 0=b rewrite canonicalSecond [] b Equal | binNatToNZero b (equalityCommutative 0=b) = refl
<BIsInherited (a :: as) [] with TotalOrder.totality ℕTotalOrder (binNatToN (a :: as)) 0
<BIsInherited (a :: as) [] | inl (inr x) with inspect (binNatToN (a :: as))
<BIsInherited (a :: as) [] | inl (inr x) | zero with≡ pr rewrite binNatToNZero (a :: as) pr | pr = exFalso (TotalOrder.irreflexive (ℕTotalOrder) x)
<BIsInherited (a :: as) [] | inl (inr x) | succ y with≡ pr rewrite pr = equalityCommutative (zeroLess' (a :: as) λ i → zeroNotSucc y (a :: as) i pr)
<BIsInherited (a :: as) [] | inr x rewrite canonicalFirst (a :: as) [] Equal | binNatToNZero (a :: as) x = refl
<BIsInherited (zero :: a) (zero :: b) = transitivity (chopDouble a b zero) (<BIsInherited a b)
<BIsInherited (zero :: a) (one :: b) with TotalOrder.totality ℕTotalOrder (binNatToN (zero :: a)) (binNatToN (one :: b))
<BIsInherited (zero :: a) (one :: b) | inl (inl 2a<2b+1) with TotalOrder.totality ℕTotalOrder (binNatToN a) (binNatToN b)
<BIsInherited (zero :: a) (one :: b) | inl (inl 2a<2b+1) | inl (inl a<b) = equalityCommutative (equalToFirstLess FirstLess a b (equalityCommutative indHyp))
    where
      t : a <BInherited b ≡ FirstLess
      t with TotalOrder.totality ℕTotalOrder (binNatToN a) (binNatToN b)
      t | inl (inl x) = refl
      t | inl (inr x) = exFalso (TotalOrder.irreflexive (ℕTotalOrder) (TotalOrder.<Transitive (ℕTotalOrder) x a<b))
      t | inr x rewrite x = exFalso (TotalOrder.irreflexive (ℕTotalOrder) a<b)
      indHyp : FirstLess ≡ go<B Equal a b
      indHyp = transitivity (equalityCommutative t) (<BIsInherited a b)
<BIsInherited (zero :: a) (one :: b) | inl (inl 2a<2b+1) | inl (inr b<a) = exFalso (noIntegersBetweenXAndSuccX {2 *N binNatToN a} (2 *N binNatToN b) (lessRespectsMultiplicationLeft (binNatToN b) (binNatToN a) 2 b<a (le 1 refl)) 2a<2b+1)
<BIsInherited (zero :: a) (one :: b) | inl (inl 2a<2b+1) | inr a=b rewrite a=b | canonicalFirst a b FirstLess | canonicalSecond (canonical a) b FirstLess | transitivity (equalityCommutative (binToBin a)) (transitivity (applyEquality NToBinNat a=b) (binToBin b)) = equalityCommutative (lemma1 (canonical b))
<BIsInherited (zero :: a) (one :: b) | inl (inr 2b+1<2a) with TotalOrder.totality ℕTotalOrder (binNatToN a) (binNatToN b)
<BIsInherited (zero :: a) (one :: b) | inl (inr 2b+1<2a) | inl (inl a<b) = exFalso (TotalOrder.irreflexive (ℕTotalOrder) (TotalOrder.<Transitive (ℕTotalOrder) 2b+1<2a (TotalOrder.<Transitive (ℕTotalOrder) (lessRespectsMultiplicationLeft (binNatToN a) (binNatToN b) 2 a<b (le 1 refl)) (le zero refl))))
<BIsInherited (zero :: a) (one :: b) | inl (inr 2b+1<2a) | inl (inr b<a) = equalityCommutative (equalToFirstGreater FirstLess a b (equalityCommutative indHyp))
  where
    t : a <BInherited b ≡ FirstGreater
    t with TotalOrder.totality ℕTotalOrder (binNatToN a) (binNatToN b)
    t | inl (inl x) = exFalso (TotalOrder.irreflexive (ℕTotalOrder) (TotalOrder.<Transitive (ℕTotalOrder) x b<a))
    t | inl (inr x) = refl
    t | inr x rewrite x = exFalso (TotalOrder.irreflexive (ℕTotalOrder) b<a)
    indHyp : FirstGreater ≡ go<B Equal a b
    indHyp = transitivity (equalityCommutative t) (<BIsInherited a b)
<BIsInherited (zero :: a) (one :: b) | inl (inr 2b+1<2a) | inr a=b rewrite a=b = exFalso (succNotLess 2b+1<2a)
<BIsInherited (zero :: a) (one :: b) | inr 2a=2b+1 = exFalso (parity (binNatToN b) (binNatToN a) (equalityCommutative 2a=2b+1))
<BIsInherited (one :: a) (zero :: b) with TotalOrder.totality ℕTotalOrder (binNatToN (one :: a)) (binNatToN (zero :: b))
<BIsInherited (one :: a) (zero :: b) | inl (inl 2a+1<2b) with TotalOrder.totality ℕTotalOrder (binNatToN a) (binNatToN b)
<BIsInherited (one :: a) (zero :: b) | inl (inl 2a+1<2b) | inl (inl a<b) = equalityCommutative (equalToFirstLess FirstGreater a b (equalityCommutative indHyp))
  where
    t : a <BInherited b ≡ FirstLess
    t with TotalOrder.totality ℕTotalOrder (binNatToN a) (binNatToN b)
    t | inl (inr x) = exFalso (TotalOrder.irreflexive (ℕTotalOrder) (TotalOrder.<Transitive (ℕTotalOrder) x a<b))
    t | inl (inl x) = refl
    t | inr x rewrite x = exFalso (TotalOrder.irreflexive (ℕTotalOrder) a<b)
    indHyp : FirstLess ≡ go<B Equal a b
    indHyp = transitivity (equalityCommutative t) (<BIsInherited a b)
<BIsInherited (one :: a) (zero :: b) | inl (inl 2a+1<2b) | inl (inr b<a) = exFalso (TotalOrder.irreflexive (ℕTotalOrder) (TotalOrder.<Transitive (ℕTotalOrder) 2a+1<2b (TotalOrder.<Transitive (ℕTotalOrder) (lessRespectsMultiplicationLeft (binNatToN b) (binNatToN a) 2 b<a (le 1 refl)) (le zero refl))))
<BIsInherited (one :: a) (zero :: b) | inl (inl 2a+1<2b) | inr a=b rewrite a=b = exFalso (succNotLess 2a+1<2b)
<BIsInherited (one :: a) (zero :: b) | inl (inr 2b<2a+1) with TotalOrder.totality ℕTotalOrder (binNatToN a) (binNatToN b)
<BIsInherited (one :: a) (zero :: b) | inl (inr 2b<2a+1) | inl (inl a<b) = exFalso (noIntegersBetweenXAndSuccX {2 *N binNatToN b} (2 *N binNatToN a) (lessRespectsMultiplicationLeft (binNatToN a) (binNatToN b) 2 a<b (le 1 refl)) 2b<2a+1)
<BIsInherited (one :: a) (zero :: b) | inl (inr 2b<2a+1) | inl (inr b<a) = equalityCommutative (equalToFirstGreater FirstGreater a b (equalityCommutative indHyp))
  where
    t : a <BInherited b ≡ FirstGreater
    t with TotalOrder.totality ℕTotalOrder (binNatToN a) (binNatToN b)
    t | inl (inl x) = exFalso (TotalOrder.irreflexive (ℕTotalOrder) (TotalOrder.<Transitive (ℕTotalOrder) x b<a))
    t | inl (inr x) = refl
    t | inr x rewrite x = exFalso (TotalOrder.irreflexive (ℕTotalOrder) b<a)
    indHyp : FirstGreater ≡ go<B Equal a b
    indHyp = transitivity (equalityCommutative t) (<BIsInherited a b)
<BIsInherited (one :: a) (zero :: b) | inl (inr 2b<2a+1) | inr a=b rewrite a=b | canonicalFirst a b FirstGreater | canonicalSecond (canonical a) b FirstGreater | transitivity (equalityCommutative (binToBin a)) (transitivity (applyEquality NToBinNat a=b) (binToBin b)) = equalityCommutative (lemma1 (canonical b))
<BIsInherited (one :: a) (zero :: b) | inr x = exFalso (parity (binNatToN a) (binNatToN b) x)
<BIsInherited (one :: a) (one :: b) = transitivity (chopDouble a b one) (<BIsInherited a b)