code: public boolean remove(Object o) {
          if (o instanceof Edge) {
              Edge e = (Edge)o;
              return (e.from() == rootVertex && vertexToEdges.remove(e.to(), e))
                  || (e.to() == rootVertex && vertexToEdges.remove(e.from(), e));            
          }
          return false;
      }
docs: {@inheritDoc}