Definition Fdigit (p : float) := digit radix (Fnum p).Definition Fshift (n : nat) (x : float) :=
  Float (Fnum x * Zpower_nat radix n) (Fexp x - n).

Theorem FdigitEq : forall x y : float, ~ is_Fzero x -> x = y :>R -> Fdigit x = Fdigit y -> x = y.