def add_sources(urls)
      urls.each_with_object( {}.compare_by_identity ) do |link, pairs|
        pairs[root_url(link)] = link
      end
    end
def add_sources(urls)
      urls.each_with_object( {}.compare_by_identity ) do |link, pairs|
        pairs[root_url(link)] = link
      end
    end
Adds root urls as hash keys