Commit 2025-01-21 04:10 33d9a863

feat: the disjoint union of smooth manifolds (#20659)

• the disjoint union of smooth manifolds is a smooth manifold
• the interior and boundary are the disjoint union of the interior and boundary; the disjoint union of boundaryless manifolds is boundaryless A future PR will prove that Sum.inl and Sum.inr between C^n manifolds are C^n. From my bordism theory branch.