360 lines
17 KiB
Text
360 lines
17 KiB
Text
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import kernel
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import macros
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variable Nat : Type
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alias ℕ : Nat
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namespace Nat
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builtin numeral
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builtin add : Nat → Nat → Nat
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infixl 65 + : add
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builtin mul : Nat → Nat → Nat
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infixl 70 * : mul
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builtin le : Nat → Nat → Bool
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infix 50 <= : le
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infix 50 ≤ : le
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definition ge (a b : Nat) := b ≤ a
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infix 50 >= : ge
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infix 50 ≥ : ge
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definition lt (a b : Nat) := a + 1 ≤ b
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infix 50 < : lt
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definition gt (a b : Nat) := b < a
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infix 50 > : gt
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definition id (a : Nat) := a
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notation 55 | _ | : id
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axiom succ_nz (a : Nat) : a + 1 ≠ 0
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axiom succ_inj {a b : Nat} (H : a + 1 = b + 1) : a = b
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axiom add_zeror (a : Nat) : a + 0 = a
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axiom add_succr (a b : Nat) : a + (b + 1) = (a + b) + 1
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axiom mul_zeror (a : Nat) : a * 0 = 0
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axiom mul_succr (a b : Nat) : a * (b + 1) = a * b + a
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axiom le_def (a b : Nat) : a ≤ b ↔ ∃ c, a + c = b
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axiom induction {P : Nat → Bool} (H1 : P 0) (H2 : ∀ (n : Nat) (iH : P n), P (n + 1)) : ∀ a, P a
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theorem induction_on {P : Nat → Bool} (a : Nat) (H1 : P 0) (H2 : ∀ (n : Nat) (iH : P n), P (n + 1)) : P a
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:= induction H1 H2 a
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theorem pred_nz {a : Nat} : a ≠ 0 → ∃ b, b + 1 = a
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:= induction_on a
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(λ H : 0 ≠ 0, false_elim (∃ b, b + 1 = 0) H)
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(λ (n : Nat) (iH : n ≠ 0 → ∃ b, b + 1 = n) (H : n + 1 ≠ 0),
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or_elim (em (n = 0))
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(λ Heq0 : n = 0, exists_intro 0 (calc 0 + 1 = n + 1 : { symm Heq0 }))
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(λ Hne0 : n ≠ 0,
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obtain (w : Nat) (Hw : w + 1 = n), from (iH Hne0),
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exists_intro (w + 1) (calc w + 1 + 1 = n + 1 : { Hw })))
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theorem discriminate {B : Bool} {a : Nat} (H1: a = 0 → B) (H2 : ∀ n, a = n + 1 → B) : B
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:= or_elim (em (a = 0))
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(λ Heq0 : a = 0, H1 Heq0)
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(λ Hne0 : a ≠ 0, obtain (w : Nat) (Hw : w + 1 = a), from (pred_nz Hne0),
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H2 w (symm Hw))
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theorem add_zerol (a : Nat) : 0 + a = a
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:= induction_on a
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(have 0 + 0 = 0 : trivial)
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(λ (n : Nat) (iH : 0 + n = n),
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calc 0 + (n + 1) = (0 + n) + 1 : add_succr 0 n
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... = n + 1 : { iH })
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theorem add_succl (a b : Nat) : (a + 1) + b = (a + b) + 1
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:= induction_on b
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(calc (a + 1) + 0 = a + 1 : add_zeror (a + 1)
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... = (a + 0) + 1 : { symm (add_zeror a) })
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(λ (n : Nat) (iH : (a + 1) + n = (a + n) + 1),
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calc (a + 1) + (n + 1) = ((a + 1) + n) + 1 : add_succr (a + 1) n
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... = ((a + n) + 1) + 1 : { iH }
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... = (a + (n + 1)) + 1 : { have (a + n) + 1 = a + (n + 1) : symm (add_succr a n) })
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theorem add_comm (a b : Nat) : a + b = b + a
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:= induction_on b
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(calc a + 0 = a : add_zeror a
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... = 0 + a : symm (add_zerol a))
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(λ (n : Nat) (iH : a + n = n + a),
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calc a + (n + 1) = (a + n) + 1 : add_succr a n
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... = (n + a) + 1 : { iH }
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... = (n + 1) + a : symm (add_succl n a))
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theorem add_assoc (a b c : Nat) : (a + b) + c = a + (b + c)
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:= symm (induction_on a
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(calc 0 + (b + c) = b + c : add_zerol (b + c)
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... = (0 + b) + c : { symm (add_zerol b) })
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(λ (n : Nat) (iH : n + (b + c) = (n + b) + c),
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calc (n + 1) + (b + c) = (n + (b + c)) + 1 : add_succl n (b + c)
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... = ((n + b) + c) + 1 : { iH }
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... = ((n + b) + 1) + c : symm (add_succl (n + b) c)
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... = ((n + 1) + b) + c : { have (n + b) + 1 = (n + 1) + b : symm (add_succl n b) }))
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theorem mul_zerol (a : Nat) : 0 * a = 0
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:= induction_on a
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(have 0 * 0 = 0 : trivial)
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(λ (n : Nat) (iH : 0 * n = 0),
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calc 0 * (n + 1) = (0 * n) + 0 : mul_succr 0 n
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... = 0 + 0 : { iH }
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... = 0 : trivial)
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theorem mul_succl (a b : Nat) : (a + 1) * b = a * b + b
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:= induction_on b
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(calc (a + 1) * 0 = 0 : mul_zeror (a + 1)
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... = a * 0 : symm (mul_zeror a)
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... = a * 0 + 0 : symm (add_zeror (a * 0)))
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(λ (n : Nat) (iH : (a + 1) * n = a * n + n),
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calc (a + 1) * (n + 1) = (a + 1) * n + (a + 1) : mul_succr (a + 1) n
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... = a * n + n + (a + 1) : { iH }
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... = a * n + n + a + 1 : symm (add_assoc (a * n + n) a 1)
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... = a * n + (n + a) + 1 : { have a * n + n + a = a * n + (n + a) : add_assoc (a * n) n a }
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... = a * n + (a + n) + 1 : { add_comm n a }
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... = a * n + a + n + 1 : { symm (add_assoc (a * n) a n) }
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... = a * (n + 1) + n + 1 : { symm (mul_succr a n) }
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... = a * (n + 1) + (n + 1) : add_assoc (a * (n + 1)) n 1)
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theorem mul_onel (a : Nat) : 1 * a = a
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:= induction_on a
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(have 1 * 0 = 0 : trivial)
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(λ (n : Nat) (iH : 1 * n = n),
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calc 1 * (n + 1) = 1 * n + 1 : mul_succr 1 n
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... = n + 1 : { iH })
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theorem mul_oner (a : Nat) : a * 1 = a
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:= induction_on a
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(have 0 * 1 = 0 : trivial)
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(λ (n : Nat) (iH : n * 1 = n),
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calc (n + 1) * 1 = n * 1 + 1 : mul_succl n 1
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... = n + 1 : { iH })
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theorem mul_comm (a b : Nat) : a * b = b * a
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:= induction_on b
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(calc a * 0 = 0 : mul_zeror a
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... = 0 * a : symm (mul_zerol a))
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(λ (n : Nat) (iH : a * n = n * a),
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calc a * (n + 1) = a * n + a : mul_succr a n
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... = n * a + a : { iH }
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... = (n + 1) * a : symm (mul_succl n a))
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theorem distributer (a b c : Nat) : a * (b + c) = a * b + a * c
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:= induction_on a
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(calc 0 * (b + c) = 0 : mul_zerol (b + c)
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... = 0 + 0 : trivial
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... = 0 * b + 0 : { symm (mul_zerol b) }
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... = 0 * b + 0 * c : { symm (mul_zerol c) })
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(λ (n : Nat) (iH : n * (b + c) = n * b + n * c),
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calc (n + 1) * (b + c) = n * (b + c) + (b + c) : mul_succl n (b + c)
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... = n * b + n * c + (b + c) : { iH }
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... = n * b + n * c + b + c : symm (add_assoc (n * b + n * c) b c)
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... = n * b + (n * c + b) + c : { add_assoc (n * b) (n * c) b }
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... = n * b + (b + n * c) + c : { add_comm (n * c) b }
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... = n * b + b + n * c + c : { symm (add_assoc (n * b) b (n * c)) }
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... = (n + 1) * b + n * c + c : { symm (mul_succl n b) }
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... = (n + 1) * b + (n * c + c) : add_assoc ((n + 1) * b) (n * c) c
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... = (n + 1) * b + (n + 1) * c : { symm (mul_succl n c) })
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theorem distributel (a b c : Nat) : (a + b) * c = a * c + b * c
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:= calc (a + b) * c = c * (a + b) : mul_comm (a + b) c
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... = c * a + c * b : distributer c a b
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... = a * c + c * b : { mul_comm c a }
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... = a * c + b * c : { mul_comm c b }
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theorem mul_assoc (a b c : Nat) : (a * b) * c = a * (b * c)
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:= symm (induction_on a
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(calc 0 * (b * c) = 0 : mul_zerol (b * c)
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... = 0 * c : symm (mul_zerol c)
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... = (0 * b) * c : { symm (mul_zerol b) })
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(λ (n : Nat) (iH : n * (b * c) = n * b * c),
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calc (n + 1) * (b * c) = n * (b * c) + (b * c) : mul_succl n (b * c)
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... = n * b * c + (b * c) : { iH }
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... = (n * b + b) * c : symm (distributel (n * b) b c)
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... = (n + 1) * b * c : { symm (mul_succl n b) }))
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theorem add_left_comm (a b c : Nat) : a + (b + c) = b + (a + c)
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:= left_comm add_comm add_assoc a b c
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theorem mul_left_comm (a b c : Nat) : a * (b * c) = b * (a * c)
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:= left_comm mul_comm mul_assoc a b c
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theorem add_injr {a b c : Nat} : a + b = a + c → b = c
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:= induction_on a
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(λ H : 0 + b = 0 + c,
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calc b = 0 + b : symm (add_zerol b)
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... = 0 + c : H
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... = c : add_zerol c)
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(λ (n : Nat) (iH : n + b = n + c → b = c) (H : n + 1 + b = n + 1 + c),
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let L1 : n + b + 1 = n + c + 1
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:= (calc n + b + 1 = n + (b + 1) : add_assoc n b 1
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... = n + (1 + b) : { add_comm b 1 }
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... = n + 1 + b : symm (add_assoc n 1 b)
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... = n + 1 + c : H
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... = n + (1 + c) : add_assoc n 1 c
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... = n + (c + 1) : { add_comm 1 c }
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... = n + c + 1 : symm (add_assoc n c 1)),
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L2 : n + b = n + c := succ_inj L1
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in iH L2)
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theorem add_injl {a b c : Nat} (H : a + b = c + b) : a = c
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:= add_injr (calc b + a = a + b : add_comm _ _
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... = c + b : H
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... = b + c : add_comm _ _)
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theorem add_eqz {a b : Nat} (H : a + b = 0) : a = 0
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:= discriminate
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(λ H1 : a = 0, H1)
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(λ (n : Nat) (H1 : a = n + 1),
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absurd_elim (a = 0)
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H (calc a + b = n + 1 + b : { H1 }
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... = n + (1 + b) : add_assoc n 1 b
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... = n + (b + 1) : { add_comm 1 b }
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... = n + b + 1 : symm (add_assoc n b 1)
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... ≠ 0 : succ_nz (n + b)))
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theorem le_intro {a b c : Nat} (H : a + c = b) : a ≤ b
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:= (symm (le_def a b)) ◂ (have (∃ x, a + x = b) : exists_intro c H)
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theorem le_elim {a b : Nat} (H : a ≤ b) : ∃ x, a + x = b
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:= (le_def a b) ◂ H
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theorem le_refl (a : Nat) : a ≤ a := le_intro (add_zeror a)
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theorem le_zero (a : Nat) : 0 ≤ a := le_intro (add_zerol a)
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theorem le_trans {a b c : Nat} (H1 : a ≤ b) (H2 : b ≤ c) : a ≤ c
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:= obtain (w1 : Nat) (Hw1 : a + w1 = b), from (le_elim H1),
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obtain (w2 : Nat) (Hw2 : b + w2 = c), from (le_elim H2),
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le_intro (calc a + (w1 + w2) = a + w1 + w2 : symm (add_assoc a w1 w2)
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... = b + w2 : { Hw1 }
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... = c : Hw2)
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theorem le_add {a b : Nat} (H : a ≤ b) (c : Nat) : a + c ≤ b + c
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:= obtain (w : Nat) (Hw : a + w = b), from (le_elim H),
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le_intro (calc a + c + w = a + (c + w) : add_assoc a c w
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... = a + (w + c) : { add_comm c w }
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... = a + w + c : symm (add_assoc a w c)
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... = b + c : { Hw })
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theorem le_antisym {a b : Nat} (H1 : a ≤ b) (H2 : b ≤ a) : a = b
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:= obtain (w1 : Nat) (Hw1 : a + w1 = b), from (le_elim H1),
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obtain (w2 : Nat) (Hw2 : b + w2 = a), from (le_elim H2),
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let L1 : w1 + w2 = 0
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:= add_injr (calc a + (w1 + w2) = a + w1 + w2 : { symm (add_assoc a w1 w2) }
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... = b + w2 : { Hw1 }
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... = a : Hw2
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... = a + 0 : symm (add_zeror a)),
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L2 : w1 = 0 := add_eqz L1
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in calc a = a + 0 : symm (add_zeror a)
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... = a + w1 : { symm L2 }
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... = b : Hw1
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theorem not_lt_0 (a : Nat) : ¬ a < 0
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:= not_intro (λ H : a + 1 ≤ 0,
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obtain (w : Nat) (Hw1 : a + 1 + w = 0), from (le_elim H),
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absurd
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(calc a + w + 1 = a + (w + 1) : add_assoc _ _ _
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... = a + (1 + w) : { add_comm _ _ }
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... = a + 1 + w : symm (add_assoc _ _ _)
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... = 0 : Hw1)
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(succ_nz (a + w)))
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theorem lt_intro {a b c : Nat} (H : a + 1 + c = b) : a < b
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:= le_intro H
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theorem lt_elim {a b : Nat} (H : a < b) : ∃ x, a + 1 + x = b
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:= le_elim H
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theorem lt_le {a b : Nat} (H : a < b) : a ≤ b
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:= obtain (w : Nat) (Hw : a + 1 + w = b), from (le_elim H),
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le_intro (calc a + (1 + w) = a + 1 + w : symm (add_assoc _ _ _)
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... = b : Hw)
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theorem lt_ne {a b : Nat} (H : a < b) : a ≠ b
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:= not_intro (λ H1 : a = b,
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obtain (w : Nat) (Hw : a + 1 + w = b), from (lt_elim H),
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absurd (calc w + 1 = 1 + w : add_comm _ _
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... = 0 :
|
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add_injr (calc b + (1 + w) = b + 1 + w : symm (add_assoc b 1 w)
|
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... = a + 1 + w : { symm H1 }
|
|||
|
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... = b : Hw
|
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... = b + 0 : symm (add_zeror b)))
|
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(succ_nz w))
|
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theorem lt_nrefl (a : Nat) : ¬ a < a
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:= not_intro (λ H : a < a,
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absurd (refl a) (lt_ne H))
|
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|
|
|
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theorem lt_trans {a b c : Nat} (H1 : a < b) (H2 : b < c) : a < c
|
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|
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:= obtain (w1 : Nat) (Hw1 : a + 1 + w1 = b), from (lt_elim H1),
|
|||
|
|
obtain (w2 : Nat) (Hw2 : b + 1 + w2 = c), from (lt_elim H2),
|
|||
|
|
lt_intro (calc a + 1 + (w1 + 1 + w2) = a + 1 + (w1 + (1 + w2)) : { add_assoc w1 1 w2 }
|
|||
|
|
... = (a + 1 + w1) + (1 + w2) : symm (add_assoc _ _ _)
|
|||
|
|
... = b + (1 + w2) : { Hw1 }
|
|||
|
|
... = b + 1 + w2 : symm (add_assoc _ _ _)
|
|||
|
|
... = c : Hw2)
|
|||
|
|
|
|||
|
|
theorem lt_le_trans {a b c : Nat} (H1 : a < b) (H2 : b ≤ c) : a < c
|
|||
|
|
:= obtain (w1 : Nat) (Hw1 : a + 1 + w1 = b), from (lt_elim H1),
|
|||
|
|
obtain (w2 : Nat) (Hw2 : b + w2 = c), from (le_elim H2),
|
|||
|
|
lt_intro (calc a + 1 + (w1 + w2) = a + 1 + w1 + w2 : symm (add_assoc _ _ _)
|
|||
|
|
... = b + w2 : { Hw1 }
|
|||
|
|
... = c : Hw2)
|
|||
|
|
|
|||
|
|
theorem le_lt_trans {a b c : Nat} (H1 : a ≤ b) (H2 : b < c) : a < c
|
|||
|
|
:= obtain (w1 : Nat) (Hw1 : a + w1 = b), from (le_elim H1),
|
|||
|
|
obtain (w2 : Nat) (Hw2 : b + 1 + w2 = c), from (lt_elim H2),
|
|||
|
|
lt_intro (calc a + 1 + (w1 + w2) = a + 1 + w1 + w2 : symm (add_assoc _ _ _)
|
|||
|
|
... = a + (1 + w1) + w2 : { add_assoc a 1 w1 }
|
|||
|
|
... = a + (w1 + 1) + w2 : { add_comm 1 w1 }
|
|||
|
|
... = a + w1 + 1 + w2 : { symm (add_assoc a w1 1) }
|
|||
|
|
... = b + 1 + w2 : { Hw1 }
|
|||
|
|
... = c : Hw2)
|
|||
|
|
|
|||
|
|
theorem ne_lt_succ {a b : Nat} (H1 : a ≠ b) (H2 : a < b + 1) : a < b
|
|||
|
|
:= obtain (w : Nat) (Hw : a + 1 + w = b + 1), from (lt_elim H2),
|
|||
|
|
let L : a + w = b := add_injl (calc a + w + 1 = a + (w + 1) : add_assoc _ _ _
|
|||
|
|
... = a + (1 + w) : { add_comm _ _ }
|
|||
|
|
... = a + 1 + w : symm (add_assoc _ _ _)
|
|||
|
|
... = b + 1 : Hw)
|
|||
|
|
in discriminate (λ Hz : w = 0, absurd_elim (a < b) (calc a = a + 0 : symm (add_zeror _)
|
|||
|
|
... = a + w : { symm Hz }
|
|||
|
|
... = b : L)
|
|||
|
|
H1)
|
|||
|
|
(λ (p : Nat) (Hp : w = p + 1), lt_intro (calc a + 1 + p = a + (1 + p) : add_assoc _ _ _
|
|||
|
|
... = a + (p + 1) : { add_comm _ _ }
|
|||
|
|
... = a + w : { symm Hp }
|
|||
|
|
... = b : L))
|
|||
|
|
|
|||
|
|
theorem strong_induction {P : Nat → Bool} (H : ∀ n, (∀ m, m < n → P m) → P n) : ∀ a, P a
|
|||
|
|
:= take a,
|
|||
|
|
let stronger : P a ∧ ∀ m, m < a → P m :=
|
|||
|
|
-- we prove a stronger result by regular induction on a
|
|||
|
|
induction_on a
|
|||
|
|
(have P 0 ∧ ∀ m, m < 0 → P m :
|
|||
|
|
let c2 : ∀ m, m < 0 → P m := λ (m : Nat) (Hlt : m < 0), absurd_elim (P m) Hlt (not_lt_0 m),
|
|||
|
|
c1 : P 0 := H 0 c2
|
|||
|
|
in and_intro c1 c2)
|
|||
|
|
(λ (n : Nat) (iH : P n ∧ ∀ m, m < n → P m),
|
|||
|
|
have P (n + 1) ∧ ∀ m, m < n + 1 → P m :
|
|||
|
|
let iH1 : P n := and_eliml iH,
|
|||
|
|
iH2 : ∀ m, m < n → P m := and_elimr iH,
|
|||
|
|
c2 : ∀ m, m < n + 1 → P m := λ (m : Nat) (Hlt : m < n + 1),
|
|||
|
|
or_elim (em (m = n))
|
|||
|
|
(λ Heq : m = n, subst iH1 (symm Heq))
|
|||
|
|
(λ Hne : m ≠ n, iH2 m (ne_lt_succ Hne Hlt)),
|
|||
|
|
c1 : P (n + 1) := H (n + 1) c2
|
|||
|
|
in and_intro c1 c2)
|
|||
|
|
in and_eliml stronger
|
|||
|
|
|
|||
|
|
set_opaque add true
|
|||
|
|
set_opaque mul true
|
|||
|
|
set_opaque le true
|
|||
|
|
set_opaque id true
|
|||
|
|
set_opaque ge true
|
|||
|
|
set_opaque lt true
|
|||
|
|
set_opaque gt true
|
|||
|
|
set_opaque id true
|
|||
|
|
end
|