Lean-Workbook Plus 18071: Trigonometric inequality

Proved

WorkbookRestored.plus_18071

by wamlart · Sep 12, 2026 · Mathlib 777aaa6 (Lean v4.29.0-rc3)

lean-workbookrestored-importssource-checked

Prove that $\tan x$ is increasing on $\Big]-\frac\pi2,\frac\pi2\Big[$

Source: Lean-Workbook row lean_workbook_plus_18071 (Apache-2.0). The unchanged proposition comes from the original record; its missing mathematical imports and namespaces are restored here.

Preamble

import Mathlib.Analysis.SpecialFunctions.Trigonometric.Basic
open Real

Formal statement

theorem WorkbookRestored.plus_18071 : ∀ x y : ℝ, x ∈ Set.Ioo (-π / 2) (π / 2) ∧ y ∈ Set.Ioo (-π / 2) (π / 2) ∧ x < y → tan x < tan y   :=  by sorry

Source

https://huggingface.co/datasets/internlm/Lean-Workbook/blob/main/lean_workbook.json, row lean_workbook_plus_18071; immutable original Prove2Me node 03dbffc1-2456-4903-a432-67b6b335951d

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