docs: def make_jvp_reversemode(fun, x):
      """Builds a function for evaluating the Jacobian-vector product at a
      point. Roughly 1.5x more FLOPs than forward-mode, plus memory requirements
      that scale with the number of primitives applied in the evaluation of f, as
      well as other overheads. See j-towns.github.io/2017/06/12/A-new-trick.html."""
      vjp, y = _make_vjp(fun, x)
      vjp_vjp, _ = _make_vjp(vjp, vspace(y).zeros())
      return vjp_vjp