// DH-nice
// class dictionary
//Cd_graph = <first> Adj <rest> Adj_list.
//Adj = <vertex> Vertex <ns> Neighbors ".".
//Neighbors: Construct | Alternat.
//Construct = "=" <c_ns> Any_vertex_list.
//Alternat = ":" <first> Vertex "|" <second> Vertex.
//Any_vertex : Labeled_vertex | Syntax_vertex.
//Syntax_vertex = <string> String.
//Labeled_vertex = "<" <label_name> Ident ">" 
//                     <class_name> Vertex.
//Adj_list: Cd_graph | Empty_cd_graph.
//Any_vertex_list: Nany_vertex_list | Empty.
//Nany_vertex_list = 
 // <first> Any_vertex <rest> Any_vertex_list.
//Empty = .
//Empty_cd_graph = .
//Vertex = <name> Ident.

Main = .

//B : C | D common <h> H.
//C = String E.
//D = H.
//H = .

X : Y | Z.
Y : Z.
Z = .