Function offset_chord_bound2 

pub fn offset_chord_bound2(
    curve: &Curve2,
    distance: Scalar,
    a: Scalar,
    b: Scalar,
) -> Option<Scalar>

Certified chord bound of the offset of a 2D curve by distance (see offset_point2) over [a, b] of the basis’s parameter. None for a basis with no derivative bound, a span with a break of the basis’s C^2 continuity strictly inside, or one whose tangent may vanish.