evalDI :: Frac MPBall -> MPBall -> MPBall
evalDI f@(Frac p q _) =
  evalDf f (Cheb.derivative p) (Cheb.derivative q)
evalDI :: Frac MPBall -> MPBall -> MPBall
evalDI f@(Frac p q _) =
  evalDf f (Cheb.derivative p) (Cheb.derivative q)
evalDI f@(Frac p q _) =
  evalDf f (Cheb.derivative p) (Cheb.derivative q)