Section Floor_Ceil.
(** Zfloor and Zceil *)
Definition Zfloor (x : R) := (up x - 1)%Z.
Definition Zceil (x : R) := (- Zfloor (- x))%Z.
Definition Ztrunc x := if Rlt_bool x 0 then Zceil x else Zfloor x.

Theorem Ztrunc_abs :
forall x,
Ztrunc (Rabs x) = Z.abs (Ztrunc x).