Euler's Formula for Simple Polyhedras $F+V-E=2$

Definition: 
A SIMPLE POLYHEDRON is a polyhedron which has no holes.

THEOREM:
Euler's Formula for Simple Polyhedra. 
If $V$ is the number of vertices, $E$ the number of edges, and $F$ the number of faces of a simple polyhedron, then $$F+V-E=2$$

Note: Most articles will quote this result for convex polyhedrons only, but it holds for those concave polyhedra without holes also.