```ruby
module ApplicationHelper

  def links_to_sentence(links)
    links.map { |o|
      link_to(o.title, o.web_url)
    }.to_sentence
  end

  def marked_up_date(date, format = :long)
    content_tag(:time, localize(date, format: format), datetime: date.iso8601)
  end

  def previous_and_next_links(document)
    siblings = {}

    if document.previous_sibling
      siblings.merge!( 
        previous_page: {
          "title" => "Previous page",
          "url" => document.previous_sibling.base_path
        }
      )
    end

    if document.next_sibling
      siblings.merge!(
        next_page: {
          "title" => "Next page",
          "url" => document.next_sibling.base_path
        }
      )
    end

    siblings
  end

end
```

Use symbols, not strings, for component object keys
user
```ruby
module ApplicationHelper

  def links_to_sentence(links)
    links.map { |o|
      link_to(o.title, o.web_url)
    }.to_sentence
  end

  def marked_up_date(date, format = :long)
    content_tag(:time, localize(date, format: format), datetime: date.iso8601)
  end

  def previous_and_next_links(document)
    siblings = {}

    if document.previous_sibling
      siblings.merge!( 
        previous_page: {
          title: "Previous page",
          url: document.previous_sibling.base_path
        }
      )
    end

    if document.next_sibling
      siblings.merge!(
        next_page: {
          title: "Next page",
          url: document.next_sibling.base_path
        }
      )
    end

    siblings
  end

end
```
assistant