A skew polygon such that every two consecutive sides (but no three) belong to a face of a regular polyhedron.
Every regular polyhedron can be orthogonally
projected onto a plane in such a way that one Petrie polygon becomes a regular
polygon with the remainder of the projection interior to it. The Petrie polygon
of the polyhedron has sides, where
The Petrie polygons shown above correspond to the Platonic
solids.
has 
sides, where
