<div id="comment:0"></div> We introduce new methods `relative_interior` and `interior`, which (in nontrivial cases) return a simple object with a `__contains__` method. Then one can write `x in P.relative_interior()` instead of `P.relative_interior_contains(x)`. This will also simplify #31660. CC: @kliem @yuan-zhou @jplab @tscrim @novoselt @orlitzky Component: **geometry** Author: **Matthias Koeppe** Branch/Commit: **[`fa4c2d2`](https://github.com/sagemath/sagetrac-mirror/commit/fa4c2d238a8f16a61f02e7cfa89ba3f17d8f4980)** Reviewer: **Jonathan Kliem** _Issue created by migration from https://trac.sagemath.org/ticket/31916_