X, Y = np.meshgrid(np.linspace(0, 5, 100), np.linspace(0, 5, 100))
F = X ** Y
G = Y ** X
fig = plt.figure()
ax = fig.add_subplot(1, 1, 1)
circ = plt.Circle((e, e), radius=0.07, color='g')
plt.contour(X, Y, F - G, [0])
ax.add_patch(circ)
plt.show()
matplotlib: add circle to plot