The Hopf Bifurcation page needs a bifurcation diagram illustration showing the supercritical case ($L_1 < 0$):

• 3D plot with $\mu$ on the horizontal axis and the $(x,y)$ phase plane on the vertical axes
• For $\mu < 0$: stable focus (spiral inward) sitting on the $\mu$-axis, drawn in blue
• At $\mu = 0$: nonlinear center (transition point)
• For $\mu > 0$: unstable focus (spiral outward), surrounded by a stable periodic orbit (drawn in pink/magenta) whose radius grows as $r = \sqrt{\mu}$
• The family of periodic orbits traces out a paraboloid opening in the $\mu > 0$ direction

A second diagram for the subcritical case ($L_1 > 0$) would also be valuable, showing the unstable periodic orbit existing for $\mu < 0$ and bounding the basin of attraction.

Reference: the lecture notes contain such a diagram (page 62, labeled $a = 1$).