Tacnodal Quartic f(x,y) = 0
and other level lines of f(x,y) = y^3 + y^2 − x^4

The level curves of the function f(x,y) = y^3 + y^2 - x^4
can be computed from the ODE: c'(t) = Rot90(grad f)(c(t))
grad f vanishes only at [x,y] = [0,0]. The Tactonal Quartic
has been studied because of its singularity at the origin.
The singularity looks like two curves touching each other.