Steiner curve | Steiner hypocycloid | tricuspoid

x(t) = a ((2 cos(t))/3 + 1/3 cos(2 t)) y(t) = a ((2 sin(t))/3 - 1/3 sin(2 t))

-6 y^2 (a^2 + 4 a x + x^2) + (a - x)^3 (a + 3 x) - 3 y^4 = 0

algebraic | closed | concave | parametric | quartic | roulette | simple

A = (2 π a^2)/9

s = (16 a)/3

d = 4