Solution
= Solution
For a positively oriented <simple closed curve> on which the vector field is nonzero, its <Poincaré index> is the total rotation of the vector field along that curve divided by $2\pi$, equivalently the <winding number> of its normalized direction. The <Poincaré index> of an isolated <fixed point> is that of a sufficiently small enclosing curve containing no other fixed point. The <index of a planar periodic orbit> is \b[$+1$].