(** * Distance *)

Definition dist_euc (x0 y0 x1 y1:R) : R :=
  sqrt (Rsqr (x0 - x1) + Rsqr (y0 - y1)).

Lemma distance_symm : forall x0 y0 x1 y1:R, dist_euc x0 y0 x1 y1 = dist_euc x1 y1 x0 y0.