Hippopede

In geometry, a hippopede (from Ancient Greek ἱπποπέδη (hippopédē) 'horse fetter') is a plane curve determined by an equation of the form

${\displaystyle (x^{2}+y^{2})^{2}=cx^{2}+dy^{2},}$

where it is assumed that c > 0 and c > d since the remaining cases either reduce to a single point or can be put into the given form with a rotation. Hippopedes are bicircular, rational, algebraic curves of degree 4 and symmetric with respect to both the x and y axes.