Section Fcore_digits.
Variable beta : radix.
Definition Zdigit n k := Z.rem (Z.quot n (Zpower beta k)) beta.

Theorem Zdigit_not_0 :
forall e n, (0 <= e)%Z ->
(Zpower beta e <= Z.abs n < Zpower beta (e + 1))%Z ->
Zdigit n e <> Z0.