Halvorsen — dx/dt = −a·x − 4·y − 4·z − y², dy/dt = −a·y − 4·z − 4·x − z², dz/dt = −a·z − 4·x − 4·y − x². RK4 cyclically symmetric 3D ODE, not Chua circuit, not Aizawa sphere, not Thomas cyclic sin, not Rössler fold, not Lorenz butterfly. Gold low-alpha trail, cap 650. RM = settled silhouette, no animate-on.