(*23*)
let fromVertice (g : IGraph) v =
    let byEdgeFromSet r =
        List.concat (List.map g.OutByEdge r)
    let exclude exclusionPredicate list =
        List.filter (fun u -> not (exclusionPredicate u)) list
    let excludeAll exclusionList list =
        exclude (fun u -> List.exists (isVertice u) exclusionList) list
    let rec fromVerticeSet r =
        let p = excludeAll r (byEdgeFromSet r)
        if p = [] then r else fromVerticeSet (p @ r)
    fromVerticeSet [v]

(*24*)
let toVertice (g : IGraph) v =
    let destReachableFrom x =
        List.exists (isVertice v) (fromVertice g x)
    let accumulateVertice acc x =
        if destReachableFrom x then x :: acc else acc
    List.fold accumulateVertice [] [0 .. g.Size-1]