http://lambdaplusjs35padjaiz4jw2fugdoeutse262phqr72uf634s2wdbqd.onion/math/1465
Let's note a0 and a1 the areas of the two shapes, b0 and b1 the border points and i0 and i1 the inner points. Let's note A the area of the new shape, B the number of border points and I the number of inner points. When merging the two shapes, 2n points that were on the border of one or the other shape become n points on the inside of the new shape.