Cruciform

A plane quartic curve also called the cross curve or policeman on point duty curve (Cundy and Rollett 1989). It is given by the implicit equation

(1)

which is equivalent to

(2)

and

(3)

In parametric form,

			(4)
			(5)

The curvature is given by

			(6)
			(7)

which, in the special case , reduces to

(8)