SOE ex.8.3
annulus :: Radius -> Radius -> Region
annulus inR outR = Shape (circle outR) `difference` Shape (circle inR)
where r1 `difference` r2 = r1 `Intersect` (Complement r2)
annulus :: Radius -> Radius -> Region
annulus inR outR = Shape (circle outR) `difference` Shape (circle inR)
where r1 `difference` r2 = r1 `Intersect` (Complement r2)