# File lib/god/dependency_graph.rb, line 9
    def add(a, b)
      node_a = self.nodes[a] || Node.new(a)
      node_b = self.nodes[b] || Node.new(b)
      
      node_a.add(node_b)
      
      self.nodes[a] ||= node_a
      self.nodes[b] ||= node_b
    end