Function stratify_branch 

pub fn stratify_branch<T, R, F>(
    graph: &Graph,
    source: &Node<T>,
    rules: &Node<R>,
    classifier: F,
    opts: GraphNodeOpts,
) -> Node<T>
where
    T: Clone + 'static,
    R: Clone + 'static,
    F: Fn(&R, &T) -> bool + 'static,

Creates or computes stratify_branch.