244 lines
No EOL
11 KiB
Text
244 lines
No EOL
11 KiB
Text
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 ≥ b)
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infix 50 < : lt
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definition gt (a b : Nat) := ¬ (a ≤ b)
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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} (a : Nat) (H1 : P 0) (H2 : ∀ (n : Nat) (iH : P n), P (n + 1)) : P a
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theorem pred::nz {a : Nat} : a ≠ 0 → ∃ b, b + 1 = a
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:= induction 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 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 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 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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:= induction 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 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 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 : 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) : symm (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 : { 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) : symm (add::assoc (a * (n + 1)) n 1))
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theorem mul::onel (a : Nat) : 1 * a = a
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:= induction 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 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 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 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 : add::assoc (n * b + n * c) b c
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... = n * b + (n * c + b) + c : { symm (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 : { 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) : symm (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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:= induction 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::inj {a b c : Nat} : a + b = a + c → b = c
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:= induction 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) : symm (add::assoc n b 1)
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... = n + (1 + b) : { add::comm b 1 }
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... = n + 1 + b : add::assoc n 1 b
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... = n + 1 + c : H
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... = n + (1 + c) : symm (add::assoc n 1 c)
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... = n + (c + 1) : { add::comm 1 c }
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... = n + c + 1 : 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::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) : symm (add::assoc n 1 b)
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... = n + (b + 1) : { add::comm 1 b }
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... = n + b + 1 : 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 : 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) : symm (add::assoc a c w)
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... = a + (w + c) : { add::comm c w }
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... = a + w + c : 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::inj (calc a + (w1 + w2) = a + w1 + w2 : { 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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set::opaque ge true
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set::opaque lt true
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set::opaque gt true
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set::opaque id true
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end |