import com.google.errorprone.annotations.DoNotMock;
import java.util.Collection;
import java.util.Set;
import javax.annotation.CheckForNull;

/**
 * An interface for <a
 * href="https://en.wikipedia.org/wiki/Graph_(discrete_mathematics)">graph</a>-structured data,
 * whose edges are anonymous entities with no identity or information of their own.
 *
 * <p>A graph is composed of a set of nodes and a set of edges connecting pairs of nodes.
 *