message: Fix "angle sum trig identity" typo
diff: @@ -3725,7 +3725,7 @@ Using the angle sum trigonometric identities:
  $$\begin{align*}
  cos(m \phi + \phi) &= cos(m \phi) cos(\phi) - sin(m \phi) sin(\phi) \Leftrightarrow C_{m + 1} = \frac{(x C_m - y S_m)}{sin(\theta)^{|m + 1|}} \\
  -sin(m \phi + \phi) &= sin(m \phi) sin(\phi) + cos(m \phi) sin(\phi) \Leftrightarrow S_{m + 1} = \frac{(x S_m - y C_m)}{sin(\theta)^{|m + 1|}}
  +sin(m \phi + \phi) &= sin(m \phi) cos(\phi) + cos(m \phi) sin(\phi) \Leftrightarrow S_{m + 1} = \frac{(x S_m - y C_m)}{sin(\theta)^{|m + 1|}}
  \end{align*}$$
  The equations above have an extra term $sin(\theta)^{-|m + 1|}$ but we can compensate for that in the $P^{|m|}_l(z)$ recursion by multiplying $P^l_l(z)$ by $sin(\theta)^{|m + 1|}$ which greatly simplifies the third equation in $\ref{shRecursions}$ because $P^l_l(cos \theta) sin(\theta)^{-l} = (-1)^l(2l - 1)!!$.
  