mirror of
https://github.com/idris-lang/Idris2.git
synced 2024-12-30 15:13:37 +03:00
341 lines
11 KiB
Idris
341 lines
11 KiB
Idris
module Data.INTEGER
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import Data.Nat
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import Syntax.PreorderReasoning
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%default total
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public export
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data INTEGER : Type where
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Z : INTEGER
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PS : Nat -> INTEGER
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NS : Nat -> INTEGER
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public export
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Cast Nat INTEGER where
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cast Z = Z
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cast (S n) = PS n
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public export
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Cast Integer INTEGER where
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cast i = case compare 0 i of
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LT => PS (cast (i - 1))
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EQ => Z
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GT => NS (cast (negate i - 1))
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public export
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Cast INTEGER Integer where
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cast Z = 0
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cast (PS n) = 1 + cast n
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cast (NS n) = negate (1 + cast n)
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public export
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Show INTEGER where
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show = show . cast {to = Integer}
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public export
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add : INTEGER -> INTEGER -> INTEGER
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add Z n = n
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add m Z = m
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add (PS m) (PS n) = PS (S (m + n))
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add (NS m) (NS n) = NS (S (m + n))
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add (PS m) (NS n) = case compare m n of
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LT => NS (minus n (S m)) -- 1+m-1-n = 1+(m-n-1)
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EQ => Z
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GT => PS (minus m (S n))
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add (NS n) (PS m) = case compare m n of
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LT => NS (minus n (S m))
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EQ => Z
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GT => PS (minus m (S n))
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public export
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mult : INTEGER -> INTEGER -> INTEGER
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mult Z n = Z
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mult m Z = Z
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mult (PS m) (PS n) = PS (m * n + m + n)
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mult (NS m) (NS n) = PS (m * n + m + n)
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mult (PS m) (NS n) = NS (m * n + m + n)
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mult (NS m) (PS n) = NS (m * n + m + n)
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public export
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Num INTEGER where
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fromInteger = cast
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(+) = add
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(*) = mult
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export
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plusZeroRightNeutral : (m : INTEGER) -> m + 0 === m
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plusZeroRightNeutral Z = Refl
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plusZeroRightNeutral (PS k) = Refl
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plusZeroRightNeutral (NS k) = Refl
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export
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plusCommutative : (m, n : INTEGER) -> m + n === n + m
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plusCommutative Z n = sym $ plusZeroRightNeutral n
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plusCommutative m Z = plusZeroRightNeutral m
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plusCommutative (PS k) (PS j) = cong (PS . S) (plusCommutative k j)
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plusCommutative (NS k) (NS j) = cong (NS . S) (plusCommutative k j)
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plusCommutative (PS k) (NS j) with (compare k j)
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_ | LT = Refl
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_ | EQ = Refl
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_ | GT = Refl
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plusCommutative (NS k) (PS j) with (compare j k)
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_ | LT = Refl
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_ | EQ = Refl
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_ | GT = Refl
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export
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castPlus : (m, n : Nat) -> the INTEGER (cast (m + n)) = cast m + cast n
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castPlus 0 n = Refl
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castPlus (S m) 0 = cong PS (plusZeroRightNeutral m)
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castPlus (S m) (S n) = cong PS (sym $ plusSuccRightSucc m n)
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public export
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Neg INTEGER where
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negate Z = Z
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negate (PS n) = NS n
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negate (NS n) = PS n
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m - n = add m (negate n)
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export
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unfoldPS : (m : Nat) -> PS m === 1 + cast m
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unfoldPS Z = Refl
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unfoldPS (S m) = Refl
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export
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unfoldNS : (m : Nat) -> NS m === - 1 - cast m
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unfoldNS Z = Refl
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unfoldNS (S m) = Refl
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export
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difference : (m, n : Nat) -> INTEGER
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difference 0 n = - cast n
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difference m 0 = cast m
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difference (S m) (S n) = difference m n
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export
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differenceZeroRight : (n : Nat) -> difference n 0 === cast n
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differenceZeroRight 0 = Refl
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differenceZeroRight (S k) = Refl
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export
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minusSuccSucc : (m, n : Nat) ->
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the INTEGER (cast (S m) - cast (S n)) === cast m - cast n
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minusSuccSucc 0 0 = Refl
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minusSuccSucc 0 (S n) = cong NS (minusZeroRight n)
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minusSuccSucc (S m) 0 = cong PS (minusZeroRight m)
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minusSuccSucc (S m) (S n) with (compare m n)
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_ | LT = Refl
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_ | EQ = Refl
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_ | GT = Refl
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export
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unfoldDifference : (m, n : Nat) -> difference m n === cast m - cast n
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unfoldDifference 0 n = Refl
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unfoldDifference m 0 = Calc $
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|~ difference m 0
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~~ cast m ...( differenceZeroRight m )
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~~ cast m + 0 ...( sym (plusZeroRightNeutral $ cast m) )
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unfoldDifference (S m) (S n) = Calc $
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|~ difference m n
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~~ cast m - cast n ...( unfoldDifference m n )
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~~ cast (S m) - cast (S n) ...( sym (minusSuccSucc m n) )
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export
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negateInvolutive : (m : INTEGER) -> - - m === m
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negateInvolutive Z = Refl
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negateInvolutive (PS k) = Refl
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negateInvolutive (NS k) = Refl
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export
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negatePlus : (m, n : INTEGER) -> - (m + n) === - m + - n
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negatePlus Z n = Refl
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negatePlus (PS k) Z = Refl
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negatePlus (NS k) Z = Refl
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negatePlus (PS k) (PS j) = Refl
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negatePlus (PS k) (NS j) with (compare k j) proof eq
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_ | LT = rewrite compareNatFlip k j in rewrite eq in Refl
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_ | EQ = rewrite compareNatFlip k j in rewrite eq in Refl
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_ | GT = rewrite compareNatFlip k j in rewrite eq in Refl
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negatePlus (NS k) (PS j) with (compare k j) proof eq
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_ | LT = rewrite compareNatFlip k j in rewrite eq in Refl
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_ | EQ = rewrite compareNatFlip k j in rewrite eq in Refl
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_ | GT = rewrite compareNatFlip k j in rewrite eq in Refl
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negatePlus (NS k) (NS j) = Refl
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export
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negateDifference : (m, n : Nat) -> - difference m n === difference n m
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negateDifference 0 n = Calc $
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|~ - - cast n
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~~ cast n ...( negateInvolutive (cast n) )
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~~ difference n 0 ...( sym (differenceZeroRight n) )
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negateDifference m 0 = cong negate (differenceZeroRight m)
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negateDifference (S m) (S n) = negateDifference m n
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plusNatDifferenceLeft : (m, n, p : Nat) ->
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cast m + difference n p === difference (m + n) p
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plusNatDifferenceLeft m 0 p = Calc $
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|~ cast m - cast p
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~~ difference m p
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...( sym (unfoldDifference m p) )
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~~ difference (m + 0) p
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...( cong (flip difference p) (sym $ plusZeroRightNeutral m) )
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plusNatDifferenceLeft m (S n) p = Calc $
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|~ cast m + difference (S n) p
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~~ PS m + difference n p
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...( sym (aux n p m) )
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~~ difference (S m + n) p
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...( plusNatDifferenceLeft (S m) n p )
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~~ difference (m + S n) p
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...( cong (flip difference p) (plusSuccRightSucc m n) )
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where
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aux : (m, n, p : Nat) -> PS p + difference m n === cast p + difference (S m) n
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aux 0 0 p = Calc $
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|~ PS p
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~~ 1 + cast p ...( unfoldPS p )
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~~ cast p + 1 ...( plusCommutative 1 (cast p) )
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aux 0 (S k) p = Calc $
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|~ PS p + NS k
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~~ difference (S p) (S k) ...( sym (unfoldDifference (S p) (S k)) )
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~~ difference p k ...( Refl )
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~~ cast p - cast k ...( unfoldDifference p k )
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aux (S k) 0 p = sym $ Calc $
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|~ cast p + PS (S k)
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~~ cast (p + S (S k)) ...( sym (castPlus p (S (S k))) )
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~~ cast (S (p + S k)) ...( cong cast (sym $ plusSuccRightSucc p (S k)) )
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~~ cast (S (S p + k)) ...( cong PS (sym $ plusSuccRightSucc p k) )
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aux (S k) (S j) p = aux k j p
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minusNatDifferenceRight : (m, n, p : Nat) ->
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- cast m + difference n p === difference n (m + p)
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minusNatDifferenceRight m n p = Calc $
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|~ - cast m + difference n p
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~~ - cast m - - difference n p
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...( cong (- cast m +) (sym $ negateInvolutive ?) )
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~~ - (cast m - difference n p)
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...( sym (negatePlus (cast m) (- difference n p)) )
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~~ - (cast m + difference p n)
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...( cong (negate . (cast m +)) (negateDifference n p) )
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~~ - (difference (m + p) n)
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...( cong negate (plusNatDifferenceLeft m p n) )
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~~ - - difference n (m + p)
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...( cong negate (sym $ negateDifference n (m + p)) )
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~~ difference n (m + p)
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...( negateInvolutive ? )
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export
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minusZeroRight : (m : INTEGER) -> m - 0 === m
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minusZeroRight = plusZeroRightNeutral
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export
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plusInverse : (m : INTEGER) -> m - m === Z
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plusInverse Z = Refl
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plusInverse (PS k) = rewrite compareNatDiag k in Refl
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plusInverse (NS k) = rewrite compareNatDiag k in Refl
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export
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plusAssociative : (m, n, p : INTEGER) -> m + (n + p) === (m + n) + p
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plusAssociative Z n p = Refl
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plusAssociative m Z p = cong (+ p) (sym $ plusZeroRightNeutral m)
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plusAssociative m n Z = Calc $
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|~ m + (n + Z)
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~~ m + n ...( cong (m +) (plusZeroRightNeutral n) )
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~~ m + n + Z ...( sym $ plusZeroRightNeutral (m + n) )
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plusAssociative (PS k) (PS j) (PS i) = cong (PS . S) $ Calc $
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|~ k + S (j + i)
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~~ S (k + (j + i)) ...( sym (plusSuccRightSucc k (j + i)) )
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~~ S ((k + j) + i) ...( cong S (plusAssociative k j i) )
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plusAssociative (PS k) (PS j) (NS i) = Calc $
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|~ PS k + (PS j - PS i)
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~~ PS k + difference (S j) (S i)
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...( cong (PS k +) (sym $ unfoldDifference (S j) (S i)) )
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~~ difference (S k + S j) (S i)
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...( plusNatDifferenceLeft (S k) (S j) (S i) )
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~~ difference (S (S (k + j))) (S i)
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...( cong (flip difference (S i)) (sym $ plusSuccRightSucc (S k) j) )
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~~ PS k + PS j - PS i
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...( unfoldDifference (S (S (k + j))) (S i) )
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plusAssociative (PS k) (NS j) (PS i) = Calc $
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|~ PS k + (NS j + PS i)
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~~ PS k + (PS i + NS j)
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...( cong (PS k +) (plusCommutative (NS j) (PS i)) )
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~~ PS k + difference (S i) (S j)
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...( cong (PS k +) (sym $ unfoldDifference (S i) (S j)) )
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~~ difference (S k + S i) (S j)
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...( plusNatDifferenceLeft (S k) (S i) (S j) )
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~~ difference (S i + S k) (S j)
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...( cong (flip difference (S j)) (plusCommutative (S k) (S i)) )
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~~ PS i + difference (S k) (S j)
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...( sym (plusNatDifferenceLeft (S i) (S k) (S j)) )
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~~ difference (S k) (S j) + PS i
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...( plusCommutative (PS i) (difference (S k) (S j)) )
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~~ PS k + NS j + PS i
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...( cong (+ PS i) (unfoldDifference (S k) (S j)) )
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plusAssociative (PS k) (NS j) (NS i) = Calc $
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|~ PS k + NS (S j + i)
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~~ difference (S k) (S (S j + i))
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...( sym (unfoldDifference (S k) (S (S j + i))) )
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~~ difference (S k) (S i + S j)
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...( cong (difference k) (plusCommutative (S j) i) )
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~~ NS i + difference (S k) (S j)
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...( sym (minusNatDifferenceRight (S i) (S k) (S j)) )
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~~ difference (S k) (S j) + NS i
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...( plusCommutative (NS i) (difference (S k) (S j)) )
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~~ (PS k + NS j) + NS i
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...( cong (+ NS i) (unfoldDifference (S k) (S j)) )
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plusAssociative (NS k) (PS j) (PS i) = Calc $
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|~ NS k + (PS j + PS i)
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~~ (PS j + PS i) + NS k
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...( plusCommutative (NS k) (PS j + PS i) )
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~~ difference (S (S (j + i))) (S k)
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...( sym (unfoldDifference (S (S (j + i))) (S k)) )
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~~ difference (S i + S j) (S k)
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...( cong (flip difference k) (plusCommutative (S j) i) )
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~~ PS i + difference (S j) (S k)
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...( sym (plusNatDifferenceLeft (S i) (S j) (S k)) )
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~~ difference (S j) (S k) + PS i
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...( plusCommutative (PS i) (difference (S j) (S k)) )
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~~ (PS j + NS k) + PS i
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...( cong (+ PS i) (unfoldDifference (S j) (S k)) )
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~~ (NS k + PS j) + PS i
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...( cong (+ PS i) (plusCommutative (PS j) (NS k)) )
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plusAssociative (NS k) (PS j) (NS i) = Calc $
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|~ NS k + (PS j + NS i)
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~~ NS k + difference (S j) (S i)
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...( cong (NS k +) (sym $ unfoldDifference (S j) (S i)) )
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~~ difference (S j) (S k + S i)
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...( minusNatDifferenceRight (S k) (S j) (S i) )
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~~ difference (S j) (S i + S k)
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...( cong (difference (S j)) (plusCommutative (S k) (S i)) )
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~~ NS i + difference (S j) (S k)
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...( sym (minusNatDifferenceRight (S i) (S j) (S k)) )
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~~ difference (S j) (S k) + NS i
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...( plusCommutative (NS i) (difference (S j) (S k)) )
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~~ (PS j + NS k) + NS i
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...( cong (+ NS i) (unfoldDifference (S j) (S k)) )
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~~ (NS k + PS j) + NS i
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...( cong (+ NS i) (plusCommutative (PS j) (NS k)) )
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plusAssociative (NS k) (NS j) (PS i) = Calc $
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|~ NS k + (NS j + PS i)
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~~ NS k + (PS i + NS j)
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...( cong (NS k +) (plusCommutative (NS j) (PS i)) )
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~~ NS k + difference (S i) (S j)
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...( cong (NS k +) (sym $ unfoldDifference (S i) (S j)) )
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~~ difference (S i) (S k + S j)
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...( minusNatDifferenceRight (S k) (S i) (S j) )
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~~ difference (S i) (S (S (k + j)))
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...( cong (difference i) (sym $ plusSuccRightSucc k j) )
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~~ PS i + (NS k + NS j)
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...( unfoldDifference (S i) (S (S (k + j))) )
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~~ (NS k + NS j) + PS i
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...( plusCommutative (PS i) (NS k + NS j) )
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plusAssociative (NS k) (NS j) (NS i) = cong (NS . S) $ Calc $
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|~ k + S (j + i)
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~~ S (k + (j + i)) ...( sym (plusSuccRightSucc k (j + i)) )
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~~ S ((k + j) + i) ...( cong S (plusAssociative k j i) )
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