conchiglie di Duerer
cartesiana

(x^2 + xy + kx - h^2)^2 = (h^2 -x^2)(x-y+k)^2

k = 0.4 (slider from -5 to 5, step 0.1)
h = 4.5 (slider from -5 to 5, step 0.1)
a: (x^(2) + x * y + k * x - h^(2))^(2) = (h^(2) - x^(2)) * (x - y + k)^(2)