Geometry nodes: Select vertex on an edge by angle

Question

I have a simple mesh, which is just an edge and i want to instance objects on some points.

1. Points, which have 3 or 4 connected edges
2. Points, which have 2 connected edges, but have 90 degree angle between them.

I managed to solve the first problem, but don't really know how to solve the second one.

Answer 1

I think it's self descriptive:

But if not, the selection is:

If the vertex has more than 2 edges, or…

…If the vertex has exactly 2 edges, and the direction from 1st to 2nd vertex of first edge is at 90° to the direction from 1st to 2nd vertex of the second edge