(** * Proposition 10 To bisect a given finite straight line. *)
(** # <div style="width:748px;height:397px;display:block" id="applet_container10"></div> # **)

(** * Proposition 11 To draw a straight line at right angles to a given straight line from a given point on it. *)
(** # <div style="width:748px;height:397px;display:block" id="applet_container11"></div> # **)
Lemma prop_11 : forall A B C, A <> B -> Col A B C -> exists F, Perp C F A B.