Retrieve nodes and edges from a graph by index.

Input parameters:

1. Gf → Graph to examine.
2. Nx → Indices of nodes to retrieve.
3. Ex → Ind of edges to retrieve.

Output parameters:

1. Pt → Points coincident with indexed graph nodes.
2. Ln → Lines coincident with indexed graph edges.
3. Bi → Boolean describing the bidirectionality of each edge.