Q:

Find remaining outer rectangles from Rectangle.Intersection

I have an outer rectangle and a rectangle inside. How can I return all remaining rectangle after cut of intersecting rectangle?

A:

The natural way to represent this would be to use the Region class, something like:
var result = new Region(outer);
result.Exclude(inner);

If you really want a list of Rectangle structures, you can look at converting to RectangleFs using GetRegionScans using an identity matrix and then converting them to Rectangles using Ceiling or Floor.

