graph

var (
	// ErrVertexNotFound is returned when an operation is requested on a
	// non-existent vertex.
	ErrVertexNotFound = errors.New("vertex not found")

	// ErrSelfLoop is returned when an operation tries to create a disallowed
	// self loop.
	ErrSelfLoop = errors.New("self loops not permitted")

	// ErrParallelEdge is returned when an operation tries to create a
	// disallowed parallel edge.
	ErrParallelEdge = errors.New("parallel edges are not permitted")
)