Definition sqrt3 := PythF 1 (PythF 1 1).

Lemma characterization_of_neq_F_bis : forall A B,
A <> B <->
let (Ac, _) := coordinates_of_point_F A in
let (Ax, Ay) := Ac in
let (Bc, _) := coordinates_of_point_F B in
let (Bx, By) := Bc in
~ (Ax =F= Bx) \/ ~ (Ay =F= By).