although non-necessarily rational, in
polar coordinates (i.e. fulfilling h(r, θ) = 0, with h algebraic), and similar phenomena for the case of surfaces. It would
be also interesting to analyze the curves defined by (implicit) expressions of the type f (r, sin(θ), cos(θ)) = 0, where f is
algebraic, since this class contains, and in fact extends, the class of algebraic curves; also, it includes the important subclass
of curves defined by equations rn = g(θ), with g(θ) a rational function, which often appear in Geometry and Physics. Some
of these questions will be explored in the future.