217 lines
9.5 KiB
Text
217 lines
9.5 KiB
Text
/-
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Copyright (c) 2015 Jeremy Avigad. All rights reserved.
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Released under Apache 2.0 license as described in the file LICENSE.
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Authors: Jeremy Avigad
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Multiplicity and prime factors. We have:
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mult p n := the greatest power of p dividing n if p > 1 and n > 0, and 0 otherwise.
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prime_factors n := the finite set of prime factors of n, assuming n > 0
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-/
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import data.nat data.finset .primes
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open eq.ops finset well_founded decidable
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namespace nat
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/- multiplicity -/
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theorem mult_rec_decreasing {p n : ℕ} (Hp : p > 1) (Hn : n > 0) : n div p < n :=
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have H' : n < n * p,
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by rewrite [-mul_one n at {1}]; apply mul_lt_mul_of_pos_left Hp Hn,
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div_lt_of_lt_mul H'
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private definition mult.F (p : ℕ) (n : ℕ) (f: Π {m : ℕ}, m < n → ℕ) : ℕ :=
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if H : (p > 1 ∧ n > 0) ∧ p ∣ n then
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succ (f (mult_rec_decreasing (and.left (and.left H)) (and.right (and.left H))))
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else 0
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definition mult (p n : ℕ) : ℕ := fix (mult.F p) n
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theorem mult_rec {p n : ℕ} (pgt1 : p > 1) (ngt0 : n > 0) (pdivn : p ∣ n) :
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mult p n = succ (mult p (n div p)) :=
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have (p > 1 ∧ n > 0) ∧ p ∣ n, from and.intro (and.intro pgt1 ngt0) pdivn,
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eq.trans (well_founded.fix_eq (mult.F p) n) (dif_pos this)
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private theorem mult_base {p n : ℕ} (H : ¬ ((p > 1 ∧ n > 0) ∧ p ∣ n)) :
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mult p n = 0 :=
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eq.trans (well_founded.fix_eq (mult.F p) n) (dif_neg H)
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theorem mult_zero_right (p : ℕ) : mult p 0 = 0 :=
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mult_base (assume H, !lt.irrefl (and.right (and.left H)))
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theorem mult_eq_zero_of_not_dvd {p n : ℕ} (H : ¬ p ∣ n) : mult p n = 0 :=
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mult_base (assume H', H (and.right H'))
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theorem mult_eq_zero_of_le_one {p : ℕ} (n : ℕ) (H : p ≤ 1) : mult p n = 0 :=
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mult_base (assume H', not_lt_of_ge H (and.left (and.left H')))
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theorem mult_zero_left (n : ℕ) : mult 0 n = 0 :=
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mult_eq_zero_of_le_one n !dec_trivial
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theorem mult_one_left (n : ℕ) : mult 1 n = 0 :=
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mult_eq_zero_of_le_one n !dec_trivial
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theorem mult_pos_of_dvd {p n : ℕ} (pgt1 : p > 1) (npos : n > 0) (pdvdn : p ∣ n) : mult p n > 0 :=
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by rewrite (mult_rec pgt1 npos pdvdn); apply succ_pos
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theorem not_dvd_of_mult_eq_zero {p n : ℕ} (pgt1 : p > 1) (npos : n > 0) (H : mult p n = 0) :
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¬ p ∣ n :=
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suppose p ∣ n,
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ne_of_gt (mult_pos_of_dvd pgt1 npos this) H
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theorem dvd_of_mult_pos {p n : ℕ} (H : mult p n > 0) : p ∣ n :=
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by_contradiction (suppose ¬ p ∣ n, ne_of_gt H (mult_eq_zero_of_not_dvd this))
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/- properties of mult -/
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theorem pow_mult_dvd (p n : ℕ) : p^(mult p n) ∣ n :=
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begin
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induction n using nat.strong_induction_on with [n, ih],
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cases eq_zero_or_pos n with [nz, npos],
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{rewrite nz, apply dvd_zero},
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cases le_or_gt p 1 with [ple1, pgt1],
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{rewrite [!mult_eq_zero_of_le_one ple1, pow_zero], apply one_dvd},
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cases (or.swap (em (p ∣ n))) with [pndvdn, pdvdn],
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{rewrite [mult_eq_zero_of_not_dvd pndvdn, pow_zero], apply one_dvd},
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show p ^ (mult p n) ∣ n, from dvd.elim pdvdn
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(take n',
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suppose n = p * n',
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have p > 0, from lt.trans zero_lt_one pgt1,
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assert n div p = n', from !div_eq_of_eq_mul_right this `n = p * n'`,
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assert n' < n,
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by rewrite -this; apply mult_rec_decreasing pgt1 npos,
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begin
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rewrite [mult_rec pgt1 npos pdvdn, `n div p = n'`, pow_succ'], subst n,
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apply mul_dvd_mul !dvd.refl,
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apply ih _ this
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end)
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end
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theorem mult_one_right (p : ℕ) : mult p 1 = 0:=
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assert H : p^(mult p 1) = 1, from eq_one_of_dvd_one !pow_mult_dvd,
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or.elim (le_or_gt p 1)
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(suppose p ≤ 1, by rewrite [!mult_eq_zero_of_le_one this])
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(suppose p > 1,
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by_contradiction
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(suppose mult p 1 ≠ 0,
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have mult p 1 > 0, from pos_of_ne_zero this,
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assert p^(mult p 1) > 1, from pow_gt_one `p > 1` this,
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show false, by rewrite H at this; apply !lt.irrefl this))
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private theorem mult_pow_mul {p n : ℕ} (i : ℕ) (pgt1 : p > 1) (npos : n > 0) :
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mult p (p^i * n) = i + mult p n :=
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begin
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induction i with [i, ih],
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rewrite [pow_zero, one_mul, zero_add], -- strange: this fails with {brackets} around it
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have ppos : p > 0, from lt.trans zero_lt_one pgt1,
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have psin_pos : p^(succ i) * n > 0, from mul_pos (!pow_pos_of_pos ppos) npos,
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have pdvd : p ∣ p^(succ i) * n, by rewrite [pow_succ', mul.assoc]; apply dvd_mul_right,
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rewrite [mult_rec pgt1 psin_pos pdvd, pow_succ, mul.right_comm, !mul_div_cancel ppos, ih],
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rewrite [add.comm i, add.comm (succ i)]
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end
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theorem mult_pow {p : ℕ} (i : ℕ) (pgt1 : p > 1) : mult p (p^i) = i :=
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by rewrite [-(mul_one (p^i)), mult_pow_mul i pgt1 zero_lt_one, mult_one_right]
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theorem le_mult {p i n : ℕ} (pgt1 : p > 1) (npos : n > 0) (pidvd : p^i ∣ n) : i ≤ mult p n :=
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dvd.elim pidvd
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(take m,
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suppose n = p^i * m,
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assert m > 0, from pos_of_mul_pos_left (this ▸ npos),
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by subst n; rewrite [mult_pow_mul i pgt1 this]; apply le_add_right)
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theorem not_dvd_div_pow_mult {p n : ℕ} (pgt1 : p > 1) (npos : n > 0) : ¬ p ∣ n div p^(mult p n) :=
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assume pdvd : p ∣ n div p^(mult p n),
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obtain m (H : n div p^(mult p n) = p * m), from exists_eq_mul_right_of_dvd pdvd,
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assert n = p^(succ (mult p n)) * m, from
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calc
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n = p^mult p n * (n div p^mult p n) : by rewrite (mul_div_cancel' !pow_mult_dvd)
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... = p^(succ (mult p n)) * m : by rewrite [H, pow_succ, mul.assoc],
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have p^(succ (mult p n)) ∣ n, by rewrite this at {2}; apply dvd_mul_right,
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have succ (mult p n) ≤ mult p n, from le_mult pgt1 npos this,
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show false, from !not_succ_le_self this
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theorem mult_mul {p m n : ℕ} (primep : prime p) (mpos : m > 0) (npos : n > 0) :
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mult p (m * n) = mult p m + mult p n :=
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let m' := m div p^mult p m, n' := n div p^mult p n in
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assert p > 1, from gt_one_of_prime primep,
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assert meq : m = p^mult p m * m', by rewrite (mul_div_cancel' !pow_mult_dvd),
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assert neq : n = p^mult p n * n', by rewrite (mul_div_cancel' !pow_mult_dvd),
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have m'pos : m' > 0, from pos_of_mul_pos_left (meq ▸ mpos),
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have n'pos : n' > 0, from pos_of_mul_pos_left (neq ▸ npos),
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have npdvdm' : ¬ p ∣ m', from !not_dvd_div_pow_mult `p > 1` mpos,
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have npdvdn' : ¬ p ∣ n', from !not_dvd_div_pow_mult `p > 1` npos,
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assert npdvdm'n' : ¬ p ∣ m' * n', from not_dvd_mul_of_prime primep npdvdm' npdvdn',
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assert m'n'pos : m' * n' > 0, from mul_pos m'pos n'pos,
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assert multm'n' : mult p (m' * n') = 0, from mult_eq_zero_of_not_dvd npdvdm'n',
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calc
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mult p (m * n) = mult p (p^(mult p m + mult p n) * (m' * n')) :
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by rewrite [pow_add, mul.right_comm, -mul.assoc, -meq, mul.assoc,
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mul.comm (n div _), -neq]
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... = mult p m + mult p n :
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by rewrite [!mult_pow_mul `p > 1` m'n'pos, multm'n']
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theorem dvd_of_forall_prime_mult_le {m n : ℕ} (mpos : m > 0)
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(H : ∀ {p}, prime p → mult p m ≤ mult p n) :
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m ∣ n :=
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begin
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revert H, revert n,
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induction m using nat.strong_induction_on with [m, ih],
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cases (decidable.em (m = 1)) with [meq, mneq],
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{intros, rewrite meq, apply one_dvd},
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have mgt1 : m > 1, from lt_of_le_of_ne (succ_le_of_lt mpos) (ne.symm mneq),
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have mge2 : m ≥ 2, from succ_le_of_lt mgt1,
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have hpd : ∃ p, prime p ∧ p ∣ m, from ex_prime_and_dvd mge2,
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cases hpd with [p, H1],
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cases H1 with [primep, pdvdm],
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intro n,
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cases (eq_zero_or_pos n) with [nz, npos],
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{intros; rewrite nz; apply dvd_zero},
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assume H : ∀ {p : ℕ}, prime p → mult p m ≤ mult p n,
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obtain m' (meq : m = p * m'), from exists_eq_mul_right_of_dvd pdvdm,
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assert pgt1 : p > 1, from gt_one_of_prime primep,
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assert m'pos : m' > 0, from pos_of_ne_zero
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(assume m'z, by revert mpos; rewrite [meq, m'z, mul_zero]; apply not_lt_zero),
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have m'ltm : m' < m,
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by rewrite [meq, -one_mul m' at {1}]; apply mul_lt_mul_of_lt_of_le m'pos pgt1 !le.refl,
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have multpm : mult p m ≥ 1, from le_mult pgt1 mpos (by rewrite pow_one; apply pdvdm),
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have multpn : mult p n ≥ 1, from le.trans multpm (H primep),
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obtain n' (neq : n = p * n'),
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from exists_eq_mul_right_of_dvd (dvd_of_mult_pos (lt_of_succ_le multpn)),
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assert n'pos : n' > 0, from pos_of_ne_zero
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(assume n'z, by revert npos; rewrite [neq, n'z, mul_zero]; apply not_lt_zero),
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have H' : ∀q, prime q → mult q m' ≤ mult q n', from
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(take q,
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assume primeq : prime q,
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have multqm : mult q m = mult q p + mult q m',
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by rewrite [meq, mult_mul primeq (pos_of_prime primep) m'pos],
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have multqn : mult q n = mult q p + mult q n',
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by rewrite [neq, mult_mul primeq (pos_of_prime primep) n'pos],
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show mult q m' ≤ mult q n', from le_of_add_le_add_left (multqm ▸ multqn ▸ H primeq)),
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assert m'dvdn' : m' ∣ n', from ih m' m'ltm m'pos n' H',
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show m ∣ n, by rewrite [meq, neq]; apply mul_dvd_mul !dvd.refl m'dvdn'
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end
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theorem eq_of_forall_prime_mult_eq {m n : ℕ} (mpos : m > 0) (npos : n > 0)
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(H : ∀ {p}, prime p → mult p m = mult p n) : m = n :=
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dvd.antisymm
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(dvd_of_forall_prime_mult_le mpos (take p, assume primep, H primep ▸ !le.refl))
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(dvd_of_forall_prime_mult_le npos (take p, assume primep, H primep ▸ !le.refl))
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/- prime factors -/
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definition prime_factors (n : ℕ) : finset ℕ := { p ∈ upto (succ n) | prime p ∧ p ∣ n }
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theorem prime_of_mem_prime_factors {p n : ℕ} (H : p ∈ prime_factors n) : prime p :=
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and.left (of_mem_filter H)
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theorem dvd_of_mem_prime_factors {p n : ℕ} (H : p ∈ prime_factors n) : p ∣ n :=
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and.right (of_mem_filter H)
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theorem mem_prime_factors {p n : ℕ} (npos : n > 0) (primep : prime p) (pdvdn : p ∣ n) :
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p ∈ prime_factors n :=
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have plen : p ≤ n, from le_of_dvd npos pdvdn,
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mem_filter_of_mem (mem_upto_of_lt (lt_succ_of_le plen)) (and.intro primep pdvdn)
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end nat
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