pub fn dual_graph(
g: &impl GraphDCEL<LinkVertex, LinkDart, LinkFace, LinkGraphIter<LinkVertex>, LinkGraphIter<LinkDart>, LinkGraphIter<LinkFace>>,
span: &Span<LinkVertex>,
) -> HashMap<LinkFace, HashSet<LinkFace>>Expand description
Returns the dual graph that doesn’t cross the edges of the span (face tree)