code: func FilterDegree(degree int, degrees map[Node]int) []Node {
  	var matching []Node
  	for n, d := range degrees {
  		if d == degree {
  			matching = append(matching, n)
  		}
  	}
  	return matching
  }
docs: // FilterDegree returns only the nodes with the desired
  // degree. This can be used with OutDegree or InDegree