pub fn post_order_from_to<G: DirectedGraph + Successors>(
graph: &G,
start_node: G::Node,
end_node: Option<G::Node>,
) -> Vec<G::Node>
pub fn post_order_from_to<G: DirectedGraph + Successors>(
graph: &G,
start_node: G::Node,
end_node: Option<G::Node>,
) -> Vec<G::Node>