Important:The networks package has been deprecated. Use the superseding package GraphTheoryinstead.

If a single argument G is passed then a table is returned.

If a single edge e is passed the either the head of e or NULL is returned depending on whether or not e is directed.

If a set of edges eset is passed then a set or list of head vertices is returned.

This routine is normally loaded via the command with(networks) but may also be referenced using the full name networks[head](...).