English
If s is contained in t, then the interior of s is contained in the interior of t.
Русский
Если s ⊆ t, то int(s) ⊆ int(t).
LaTeX
$$$ \forall X [TopologicalSpace X], \forall s,t \subseteq X, s \subseteq t \Rightarrow \operatorname{int}(s) \subseteq \operatorname{int}(t)$$$
Lean4
@[mono, gcongr]
theorem interior_mono (h : s ⊆ t) : interior s ⊆ interior t :=
interior_maximal (Subset.trans interior_subset h) isOpen_interior