message: Fix error spotted by Matthew
diff: @@ -6,8 +6,8 @@ It was discovered by [Gauss](https://en.wikipedia.org/wiki/Carl_Friedrich_Gauss)
  The heart of Cooley-Tukey FFT is actually about converting between coefficient and evaluation representations, rather than the multiplication itself.
  Given polynomials $p$ and $q$ in dense coefficient representation, it works like this.
  1. Convert $p$ and $q$ from coefficient to evaluation form in $O(n\log n)$ using Cooley-Tukey FFT
  -2. Multiply $p$ and $q$ in evaluation form by multiplying their points pairwise in $O(n)$
  -3. Convert $p$ and $q$ back to to coefficient form in $O(n\log n)$ using the inverse Cooley-Tukey FFT
  +2. Compute $r = p*q$ in evaluation form by multiplying their points pairwise in $O(n)$
  +3. Convert $r$ back to to coefficient form in $O(n\log n)$ using the inverse Cooley-Tukey FFT
  The key observation is that we can choose any $n$ distinct evaluation points to represent any degree $n - 1$ polynomial.
  The Cooley-Tukey FFT works by selecting points that yield an efficient FFT algorithm. These points are fixed and work for any polynomials of a given degree.
  