To quickly illustrate 'perpendicular', take a pen and place one end on a table so that the pen is standing up.  The table surface is the polygon.  The long dimension of the pen is perpendicular to the table's surface and could be used to represent the table surface's normal. :)

C makes it easy to shoot yourself in the foot. C++ makes it harder, but when you do, you blow your whole leg off.

 -- Bjarne Stroustrup

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