(LearnerND) flat simplices are sometimes added on the surface of the triangulation

## ([original issue on GitLab](https://gitlab.kwant-project.org/qt/adaptive/issues/111))

_opened by Jorn Hoofwijk ([@Jorn](https://gitlab.kwant-project.org/Jorn)) at 2018-10-08T17:01:03.791Z_

In some notebook I wrote I noticed that sometimes there are (almost) flat simplices on the surface of the convex hull of the triangulation.