English
If f is concave on a ball and bounded in absolute value by M, then f is Lipschitz on a smaller ball with some finite constant.
Русский
Если f конкавна на шаре и ограничена сверху- снизу по модулю величины M, то на меньшем шаре f липшицево ограничена.
LaTeX
$$$\\exists K,\\; \\text{LipschitzOnWith}(K)\n f\\; (\\mathrm{ball}\\ x_0, r')$$$
Lean4
theorem lipschitzOnWith_of_abs_le (hf : ConcaveOn ℝ (ball x₀ r) f) (hε : 0 < ε) (hM : ∀ a, dist a x₀ < r → |f a| ≤ M) :
LipschitzOnWith (2 * M / ε).toNNReal f (ball x₀ (r - ε)) := by
simpa using hf.neg.lipschitzOnWith_of_abs_le hε <| by simpa using hM