# File lib/nanoc/base/directed_graph.rb, line 119
    def delete_edges_from(from)
      return if @from_graph[from].nil?

      @from_graph[from].each do |to|
        @to_graph[to].delete(from)
        @roots.add(to) if @to_graph[to].empty?
      end
      @from_graph.delete(from)
    end