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

(* Specifications: *)
Theorem Zdigit_lt :
forall n k,
(k < 0)%Z ->
Zdigit n k = Z0.
Theorem Zdigit_0 :
forall k, Zdigit 0 k = Z0.
Theorem Zdigit_opp :
forall n k,
Zdigit (-n) k = Zopp (Zdigit n k).
Theorem Zdigit_ge_Zpower_pos :
forall e n,
(0 <= n < Zpower beta e)%Z ->
forall k, (e <= k)%Z -> Zdigit n k = Z0.
Theorem Zdigit_ge_Zpower :
forall e n,
(Zabs n < Zpower beta e)%Z ->
forall k, (e <= k)%Z -> Zdigit n k = Z0.
Theorem Zdigit_not_0_pos :
forall e n, (0 <= e)%Z ->
(Zpower beta e <= n < Zpower beta (e + 1))%Z ->
Zdigit n e <> Z0.
Theorem Zdigit_not_0 :
forall e n, (0 <= e)%Z ->
(Zpower beta e <= Zabs n < Zpower beta (e + 1))%Z ->
Zdigit n e <> Z0.
Theorem Zdigit_mul_pow :
forall n k k', (0 <= k')%Z ->
Zdigit (n * Zpower beta k') k = Zdigit n (k - k').
Theorem Zdigit_div_pow :
forall n k k', (0 <= k)%Z -> (0 <= k')%Z ->
Zdigit (Z.quot n (Zpower beta k')) k = Zdigit n (k + k').
Theorem Zdigit_mod_pow :
forall n k k', (k < k')%Z ->
Zdigit (Z.rem n (Zpower beta k')) k = Zdigit n k.
Theorem Zdigit_mod_pow_out :
forall n k k', (0 <= k' <= k)%Z ->
Zdigit (Z.rem n (Zpower beta k')) k = Z0.