We are allowed to assume that any polygon, convex or not, can
be split into a finite number of nonoverlapping triangles.
However in this proof we assume that the interior of the
polygon does not have any holes like the red polygon shown with a
yellow hole in the diagram. Pick's formula is related to Euler's
formula and ${\rm area }(P) = i + {1\over 2}p  q$ where $q$
depends on the number of holes.
