code: func hasMorphism(via interface{}, rev bool, nodes ...quad.Value) morphism {
  	var node shape.Shape
  	if len(nodes) == 0 {
  		node = shape.AllNodes{}
  	} else {
  		node = shape.Lookup(nodes)
  	}
  	return hasShapeMorphism(via, rev, node)
  }
docs: // hasMorphism is the set of nodes that is reachable via either a *Path, a
  // single node.(string) or a list of nodes.([]string).