English
If a function f is monotone on a set s and s2 is a subset of s, then f is monotone on s2.
Русский
Если функция f монотонна на множестве s и s2 ⊆ s, то f монотонна на s2.
LaTeX
$$$\operatorname{MonotoneOn}(f,s) \to (s_2 \subseteq s) \to \operatorname{MonotoneOn}(f,s_2)$$$
Lean4
theorem _root_.MonotoneOn.mono (h : MonotoneOn f s) (h' : s₂ ⊆ s) : MonotoneOn f s₂ := fun _ hx _ hy =>
h (h' hx) (h' hy)