graph

var (
	ErrNilGraph          = errors.New("cannot operate on nil-graph")
	ErrNilNode           = errors.New("cannot operate on nil-node")
	ErrNodeAlreadyExists = errors.New("node with identical hash already exists in graph")
	ErrNodeNotFound      = errors.New("node not found")
	ErrEdgeSelf          = errors.New("self-edges are not allowed")
	ErrEdgeCrossLevel    = errors.New("edges not allowed between nodes of different hierarchical levels")
)