diff --git a/FormalConjectures/Books/BugeaudDistributionsModuloOne/IntDistanceDistribution.lean b/FormalConjectures/Books/BugeaudDistributionsModuloOne/IntDistanceDistribution.lean new file mode 100644 index 0000000000..32bf7b388f --- /dev/null +++ b/FormalConjectures/Books/BugeaudDistributionsModuloOne/IntDistanceDistribution.lean @@ -0,0 +1,95 @@ +/- +Copyright 2026 The Formal Conjectures Authors. + +Licensed under the Apache License, Version 2.0 (the "License"); +you may not use this file except in compliance with the License. +You may obtain a copy of the License at + + https://www.apache.org/licenses/LICENSE-2.0 + +Unless required by applicable law or agreed to in writing, software +distributed under the License is distributed on an "AS IS" BASIS, +WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. +See the License for the specific language governing permissions and +limitations under the License. +-/ + +import FormalConjectures.Util.ProblemImports +import FormalConjecturesForMathlib.Data.Real.NearestInt +/-! +# Bugeaud Collection of Conjectures and Open Questions: Fractional Parts of Powers + +Chapter 10 of the book collects open questions. This file formalizes Problems 10.1, +10.2, 10.3 and the unnumbered conjecture by Waldschmidt. + +*References:* + - [Bug12] Bugeaud, Yann. "Distribution modulo one and Diophantine approximation." + Vol. 193. Cambridge University Press, 2012. Chapter 10. + - [Har19] Hardy, Gr H. "A problem of Diophantine approximation." + J. Indian Math. Soc 11 (1919): 162-166. + - [Kok45] Koksma, J. F. "Sur la théorie métrique des approximations diophantiques." + Indag. Math 7 (1945): 54-70. + - [Mah53] Mahler, Kurt. "On the approximation of logarithms of algebraic numbers." + Philosophical Transactions of the Royal Society of London. Series A, + Mathematical and Physical Sciences 245.898 (1953): 371-398. + - [Wal03](http://webusers.imj-prg.fr/~michel.waldschmidt/articles/pdf/Cetraro.pdf) + Waldschmidt, Michel. "Linear independence measures for logarithms of algebraic numbers." + Diophantine Approximation: Lectures given at the CIME Summer School held in Cetraro, Italy, + June 28–July 6, 2000. Berlin, Heidelberg: Springer Berlin Heidelberg, 2003. 249-344. +-/ + +namespace Bugeaud + +/-- +Problem 10.1. Are there a transcendental number $\alpha$ and a positive real +number $\xi$ such that $\lVert \xi \alpha^n \rVert$ tends to~$0$ as~$n$ tends to infinity? [Har19] +(Trivial for $|\alpha| < 1$) +-/ +@[category research open, AMS 11] +theorem problem_10_1 : answer(sorry) ↔ + ∃ (α ξ : ℝ), 1 < |α| ∧ Transcendental ℚ α ∧ 0 < ξ ∧ + Filter.Tendsto (fun n : ℕ ↦ distToNearestInt (ξ * α ^ n)) Filter.atTop (nhds 0) := by + sorry + +/-- +Problem 10.2. To prove that $\lVert e^n \rVert$ does not tend to 0 as n tends to +infinity. +-/ +@[category research open, AMS 11] +theorem problem_10_2 : + ¬ Filter.Tendsto (fun n : ℕ ↦ distToNearestInt (Real.exp n)) Filter.atTop (nhds 0) := by + sorry + +/-- +Problem 10.3. To prove that there exists a positive real number~$c$ such +that $\lVert e^n \rVert > e^{−cn}$, for every~$n \ge 1$. Posed by Mahler [Mah53]. +-/ +@[category research open, AMS 11] +theorem problem_10_3 : + ∃ c : ℝ, 0 < c ∧ ∀ n : ℕ, 1 ≤ n → Real.exp (-c * n) < distToNearestInt (Real.exp n) := by + sorry + +/-- +Waldschmidt [Wal03] conjectured that a stronger result holds, namely +that there exists a positive real number~$c$ such that $\lVert e^n \rVert > n^{−c}$ for +every~$n \ge 1$. This is supported by metrical results [Kok45]. +-/ +@[category research open, AMS 11] +theorem waldschmidt : + ∃ c : ℝ, 0 < c ∧ ∀ n : ℕ, 1 ≤ n → (n : ℝ) ^ (-c) < distToNearestInt (Real.exp n) := by + sorry + +/-- +Waldschmidt's conjecture is stronger than Mahler's: since $\log n \le n$ for $n \ge 1$, +the polynomial lower bound $n^{-c}$ dominates the exponential lower bound $e^{-cn}$. +-/ +@[category test, AMS 11] +theorem problem_10_3_of_waldschmidt (h : type_of% waldschmidt) : type_of% problem_10_3 := by + obtain ⟨c, hc, hyp⟩ := h + refine ⟨c, hc, fun n hn => ?_⟩ + have hn_pos : (0 : ℝ) < n := by exact_mod_cast hn + refine lt_of_le_of_lt ?_ (hyp n hn) + rw [Real.rpow_def_of_pos hn_pos] + exact Real.exp_le_exp.mpr (by nlinarith [Real.log_le_self hn_pos.le]) + +end Bugeaud