Let $M^n$ ($n=3$ if needed) be a smooth manifold and $K \subset M$ be a compact submamifold diffeomorphic to the $n$-disk, satisfying $K \subset U$, for some chart $(\varphi,U).$
Consider a compact submanifold $N^n\subset M^n $ with boundary such that
- $\text {Int }N^n \cap \text {Int}K \neq \emptyset,$
- $N^n \cap K$ is connected.
I would like to know if there exists a compact smooth manifold $L\subset U $ with boundary such that the following properties hold
- $K\subset L$,
- $L \cup N $ is a smooth manifold with boundary,
- $L\cap N $ is a smooth manifold with boundary.
This result seems true, however, I was not able to prove it. Can anyone help me?
I think it is always possible to do something like the picture below
