lean2/library/data/pnat.lean
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/-
Copyright (c) 2015 Robert Y. Lewis. All rights reserved.
Released under Apache 2.0 license as described in the file LICENSE.
Author: Robert Y. Lewis
Basic facts about the positive natural numbers.
Developed primarily for use in the construction of . For the most part, the only theorems here
are those needed for that construction.
-/
import data.rat.order data.nat
open nat rat subtype eq.ops
open - [notations] algebra
namespace pnat
definition pnat := { n : | n > 0 }
notation `+` := pnat
definition pos (n : ) (H : n > 0) : + := tag n H
definition nat_of_pnat (p : +) : := elt_of p
reserve postfix `~`:std.prec.max_plus
local postfix ~ := nat_of_pnat
theorem pnat_pos (p : +) : p~ > 0 := has_property p
definition add (p q : +) : + :=
tag (p~ + q~) (nat.add_pos (pnat_pos p) (pnat_pos q))
infix + := add
definition mul (p q : +) : + :=
tag (p~ * q~) (nat.mul_pos (pnat_pos p) (pnat_pos q))
infix * := mul
definition le (p q : +) := p~ ≤ q~
infix ≤ := le
notation p ≥ q := q ≤ p
definition lt (p q : +) := p~ < q~
infix < := lt
protected theorem pnat.eq {p q : +} : p~ = q~ → p = q :=
subtype.eq
definition pnat_le_decidable [instance] (p q : +) : decidable (p ≤ q) :=
nat.decidable_le p~ q~
definition pnat_lt_decidable [instance] {p q : +} : decidable (p < q) :=
nat.decidable_lt p~ q~
theorem le.trans {p q r : +} (H1 : p ≤ q) (H2 : q ≤ r) : p ≤ r := nat.le.trans H1 H2
definition max (p q : +) :=
tag (nat.max p~ q~) (nat.lt_of_lt_of_le (!pnat_pos) (!le_max_right))
theorem max_right (a b : +) : max a b ≥ b := !le_max_right
theorem max_left (a b : +) : max a b ≥ a := !le_max_left
theorem max_eq_right {a b : +} (H : a < b) : max a b = b :=
pnat.eq (nat.max_eq_right_of_lt H)
theorem max_eq_left {a b : +} (H : ¬ a < b) : max a b = a :=
pnat.eq (nat.max_eq_left (le_of_not_gt H))
theorem le_of_lt {a b : +} : a < b → a ≤ b := nat.le_of_lt
theorem not_lt_of_ge {a b : +} : a ≤ b → ¬ (b < a) := nat.not_lt_of_ge
theorem le_of_not_gt {a b : +} : ¬ a < b → b ≤ a := nat.le_of_not_gt
theorem eq_of_le_of_ge {a b : +} (H1 : a ≤ b) (H2 : b ≤ a) : a = b :=
pnat.eq (nat.eq_of_le_of_ge H1 H2)
theorem le.refl (a : +) : a ≤ a := !nat.le.refl
notation 2 := (tag 2 dec_trivial : +)
notation 3 := (tag 3 dec_trivial : +)
definition pone : + := tag 1 dec_trivial
definition rat_of_pnat [reducible] (n : +) : := n~
theorem pnat.to_rat_of_nat (n : +) : rat_of_pnat n = of_nat n~ := rfl
-- these will come in rat
theorem rat_of_nat_nonneg (n : ) : 0 ≤ of_nat n := trivial
theorem rat_of_pnat_ge_one (n : +) : rat_of_pnat n ≥ 1 :=
of_nat_le_of_nat_of_le (pnat_pos n)
theorem rat_of_pnat_is_pos (n : +) : rat_of_pnat n > 0 :=
of_nat_lt_of_nat_of_lt (pnat_pos n)
theorem of_nat_le_of_nat_of_le {m n : } (H : m ≤ n) : of_nat m ≤ of_nat n :=
of_nat_le_of_nat_of_le H
theorem of_nat_lt_of_nat_of_lt {m n : } (H : m < n) : of_nat m < of_nat n :=
of_nat_lt_of_nat_of_lt H
theorem rat_of_pnat_le_of_pnat_le {m n : +} (H : m ≤ n) : rat_of_pnat m ≤ rat_of_pnat n :=
of_nat_le_of_nat_of_le H
theorem rat_of_pnat_lt_of_pnat_lt {m n : +} (H : m < n) : rat_of_pnat m < rat_of_pnat n :=
of_nat_lt_of_nat_of_lt H
theorem pnat_le_of_rat_of_pnat_le {m n : +} (H : rat_of_pnat m ≤ rat_of_pnat n) : m ≤ n :=
le_of_of_nat_le_of_nat H
definition inv (n : +) : := (1 : ) / rat_of_pnat n
postfix `⁻¹` := inv
theorem inv_pos (n : +) : n⁻¹ > 0 := one_div_pos_of_pos !rat_of_pnat_is_pos
theorem inv_le_one (n : +) : n⁻¹ ≤ (1 : ) :=
begin
rewrite [↑inv, -one_div_one],
apply one_div_le_one_div_of_le,
apply rat.zero_lt_one,
apply rat_of_pnat_ge_one
end
theorem inv_lt_one_of_gt {n : +} (H : n~ > 1) : n⁻¹ < (1 : ) :=
begin
rewrite [↑inv, -one_div_one],
apply one_div_lt_one_div_of_lt,
apply rat.zero_lt_one,
rewrite pnat.to_rat_of_nat,
apply (of_nat_lt_of_nat_of_lt H)
end
theorem pone_inv : pone⁻¹ = 1 := rfl
theorem add_invs_nonneg (m n : +) : 0 ≤ m⁻¹ + n⁻¹ :=
begin
apply rat.le_of_lt,
apply rat.add_pos,
repeat apply inv_pos
end
theorem one_mul (n : +) : pone * n = n :=
begin
apply pnat.eq,
rewrite [↑pone, ↑mul, ↑nat_of_pnat, one_mul]
end
theorem pone_le (n : +) : pone ≤ n :=
succ_le_of_lt (pnat_pos n)
theorem pnat_to_rat_mul (a b : +) : rat_of_pnat (a * b) = rat_of_pnat a * rat_of_pnat b := rfl
theorem mul_lt_mul_left (a b c : +) (H : a < b) : a * c < b * c :=
nat.mul_lt_mul_of_pos_right H !pnat_pos
theorem one_lt_two : pone < 2 := !nat.le.refl
theorem inv_two_mul_lt_inv (n : +) : (2 * n)⁻¹ < n⁻¹ :=
begin
rewrite ↑inv,
apply one_div_lt_one_div_of_lt,
apply rat_of_pnat_is_pos,
have H : n~ < (2 * n)~, begin
rewrite -one_mul at {1},
apply mul_lt_mul_left,
apply one_lt_two
end,
apply of_nat_lt_of_nat_of_lt,
apply H
end
theorem inv_two_mul_le_inv (n : +) : (2 * n)⁻¹ ≤ n⁻¹ := rat.le_of_lt !inv_two_mul_lt_inv
theorem inv_ge_of_le {p q : +} (H : p ≤ q) : q⁻¹ ≤ p⁻¹ :=
one_div_le_one_div_of_le !rat_of_pnat_is_pos (rat_of_pnat_le_of_pnat_le H)
theorem inv_gt_of_lt {p q : +} (H : p < q) : q⁻¹ < p⁻¹ :=
one_div_lt_one_div_of_lt !rat_of_pnat_is_pos (rat_of_pnat_lt_of_pnat_lt H)
theorem ge_of_inv_le {p q : +} (H : p⁻¹ ≤ q⁻¹) : q ≤ p :=
pnat_le_of_rat_of_pnat_le (le_of_one_div_le_one_div !rat_of_pnat_is_pos H)
theorem two_mul (p : +) : rat_of_pnat (2 * p) = (1 + 1) * rat_of_pnat p :=
by rewrite pnat_to_rat_mul
theorem add_halves (p : +) : (2 * p)⁻¹ + (2 * p)⁻¹ = p⁻¹ :=
begin
rewrite [↑inv, -(@add_halves (1 / (rat_of_pnat p))), rat.div_div_eq_div_mul],
have H : rat_of_pnat (2 * p) = rat_of_pnat p * (1 + 1), by rewrite [rat.mul.comm, two_mul],
rewrite *H
end
theorem add_halves_double (m n : +) :
m⁻¹ + n⁻¹ = ((2 * m)⁻¹ + (2 * n)⁻¹) + ((2 * m)⁻¹ + (2 * n)⁻¹) :=
have hsimp [visible] : ∀ a b : , (a + a) + (b + b) = (a + b) + (a + b),
by intros; rewrite [rat.add.assoc, -(rat.add.assoc a b b), {_+b}rat.add.comm, -*rat.add.assoc],
by rewrite [-add_halves m, -add_halves n, hsimp]
theorem inv_mul_eq_mul_inv {p q : +} : (p * q)⁻¹ = p⁻¹ * q⁻¹ :=
by rewrite [↑inv, pnat_to_rat_mul, one_div_mul_one_div]
theorem inv_mul_le_inv (p q : +) : (p * q)⁻¹ ≤ q⁻¹ :=
begin
rewrite [inv_mul_eq_mul_inv, -{q⁻¹}rat.one_mul at {2}],
apply rat.mul_le_mul,
apply inv_le_one,
apply rat.le.refl,
apply rat.le_of_lt,
apply inv_pos,
apply rat.le_of_lt rat.zero_lt_one
end
theorem pnat_mul_le_mul_left' (a b c : +) (H : a ≤ b) : c * a ≤ c * b :=
nat.mul_le_mul_of_nonneg_left H (nat.le_of_lt !pnat_pos)
theorem mul.assoc (a b c : +) : a * b * c = a * (b * c) :=
pnat.eq !nat.mul.assoc
theorem mul.comm (a b : +) : a * b = b * a :=
pnat.eq !nat.mul.comm
theorem add.assoc (a b c : +) : a + b + c = a + (b + c) :=
pnat.eq !nat.add.assoc
theorem mul_le_mul_left (p q : +) : q ≤ p * q :=
begin
rewrite [-one_mul at {1}, mul.comm, mul.comm p],
apply pnat_mul_le_mul_left',
apply pone_le
end
theorem mul_le_mul_right (p q : +) : p ≤ p * q :=
by rewrite mul.comm; apply mul_le_mul_left
theorem pnat.lt_of_not_le {p q : +} (H : ¬ p ≤ q) : q < p :=
nat.lt_of_not_ge H
theorem inv_cancel_left (p : +) : rat_of_pnat p * p⁻¹ = (1 : ) :=
mul_one_div_cancel (ne.symm (rat.ne_of_lt !rat_of_pnat_is_pos))
theorem inv_cancel_right (p : +) : p⁻¹ * rat_of_pnat p = (1 : ) :=
by rewrite rat.mul.comm; apply inv_cancel_left
theorem lt_add_left (p q : +) : p < p + q :=
begin
have H : p~ < p~ + q~, begin
rewrite -nat.add_zero at {1},
apply nat.add_lt_add_left,
apply pnat_pos
end,
apply H
end
theorem inv_add_lt_left (p q : +) : (p + q)⁻¹ < p⁻¹ :=
by apply inv_gt_of_lt; apply lt_add_left
theorem div_le_pnat (q : ) (n : +) (H : q ≥ n⁻¹) : 1 / q ≤ rat_of_pnat n :=
begin
apply rat.div_le_of_le_mul,
apply rat.lt_of_lt_of_le,
apply inv_pos,
rotate 1,
apply H,
apply rat.le_mul_of_div_le,
apply rat_of_pnat_is_pos,
apply H
end
theorem pnat_cancel' (n m : +) : (n * n * m)⁻¹ * (rat_of_pnat n * rat_of_pnat n) = m⁻¹ :=
assert hsimp : ∀ a b c : , (a * a * (b * b * c)) = (a * b) * (a * b) * c, from
λa b c, by rewrite[-*rat.mul.assoc]; exact (!rat.mul.right_comm ▸ rfl),
by rewrite [rat.mul.comm, *inv_mul_eq_mul_inv, hsimp, *inv_cancel_left, *rat.one_mul]
definition pceil (a : ) : + := tag (ubound a) !ubound_pos
theorem pceil_helper {a : } {n : +} (H : pceil a ≤ n) (Ha : a > 0) : n⁻¹ ≤ 1 / a :=
rat.le.trans (inv_ge_of_le H) (one_div_le_one_div_of_le Ha (ubound_ge a))
theorem inv_pceil_div (a b : ) (Ha : a > 0) (Hb : b > 0) : (pceil (a / b))⁻¹ ≤ b / a :=
!one_div_one_div ▸ one_div_le_one_div_of_le
(one_div_pos_of_pos (div_pos_of_pos_of_pos Hb Ha))
(!div_div_eq_mul_div⁻¹ ▸ !rat.one_mul⁻¹ ▸ !ubound_ge)
theorem sep_by_inv {a b : } (H : a > b) : ∃ N : +, a > (b + N⁻¹ + N⁻¹) :=
begin
apply exists.elim (exists_add_lt_and_pos_of_lt H),
intro c Hc,
existsi (pceil ((1 + 1 + 1) / c)),
apply rat.lt.trans,
rotate 1,
apply and.left Hc,
rewrite rat.add.assoc,
apply rat.add_lt_add_left,
rewrite -(@rat.add_halves c) at {3},
apply rat.add_lt_add,
repeat (apply rat.lt_of_le_of_lt;
apply inv_pceil_div;
apply dec_trivial;
apply and.right Hc;
apply div_lt_div_of_pos_of_lt_of_pos;
repeat (apply two_pos);
apply and.right Hc)
end
theorem nonneg_of_ge_neg_invs (a : ) (H : ∀ n : +, -n⁻¹ ≤ a) : 0 ≤ a :=
rat.le_of_not_gt (suppose a < 0,
have H2 : 0 < -a, from neg_pos_of_neg this,
(rat.not_lt_of_ge !H) (iff.mp !lt_neg_iff_lt_neg (calc
(pceil (of_num 2 / -a))⁻¹ ≤ -a / of_num 2
: !inv_pceil_div dec_trivial H2
... < -a / 1
: div_lt_div_of_pos_of_lt_of_pos dec_trivial dec_trivial H2
... = -a : !div_one)))
theorem pnat_bound {ε : } (Hε : ε > 0) : ∃ p : +, p⁻¹ ≤ ε :=
begin
existsi (pceil (1 / ε)),
rewrite -(rat.one_div_one_div ε) at {2},
apply pceil_helper,
apply le.refl,
apply one_div_pos_of_pos Hε
end
theorem p_add_fractions (n : +) : (2 * n)⁻¹ + (2 * 3 * n)⁻¹ + (3 * n)⁻¹ = n⁻¹ :=
assert T : 2⁻¹ + 2⁻¹ * 3⁻¹ + 3⁻¹ = 1, from dec_trivial,
by rewrite[*inv_mul_eq_mul_inv,-*rat.right_distrib,T,rat.one_mul]
theorem rat_power_two_le (k : +) : rat_of_pnat k ≤ rat.pow 2 k~ :=
!binary_nat_bound
end pnat