The General Schoenflies Theorem and Cantrell's Theorem

This time we're going to show that an embedded $(n-1)$-sphere in $\mathbb R^n$ is flat if it is bicollared (the generalized Schoenflies Theorem of B. Mazur and M. Brown) or if $n>3$ and the sphere has a "bicollar pinched at one point" (Cantrell's Theorem). Some lemmas proved last time will be used.

Zoom: https://mi-ras-ru.zoom.us/j/91599052030
Access code: the Euler characteristic of the wedge of two circles
(the password is not the specified phrase but the number that it determines)