<% if @publication.parts.size > 1 then %>
<aside>
  <div class="inner">
    <nav role="navigation" class="page-navigation">
      <% @publication.parts.each_slice(parts_group_size(@publication.parts)).with_index do |parts,i| %>
        <ol<%= " start=\"#{parts_group_size(@publication.parts) + 1}\"".html_safe if i == 1 %>>
          <% parts.each do |nav_part| %>
            <% if @publication.current_part == nav_part %>
              <li class="active">
                <%= nav_part.title %>
              </li>
            <% else %>
              <li>
                <%= link_to nav_part.title, part_path(@publication.slug, nav_part.slug, @edition), :title => "#{ t 'formats.guide.part' } #{ part_number @publication.parts, nav_part }: #{ nav_part.title }" %>
              </li>
            <% end %>
          <% end %>
        </ol>
      <% end %>
    </nav>
  </div>
</aside>
<% end %>

<% if @publication.parts.size > 1 then %>
<aside>
  <div class="inner">
    <nav role="navigation" class="page-navigation">
      <% @publication.parts.each_slice(parts_group_size(@publication.parts)).with_index do |parts,i| %>
        <ol<%= " start=\"#{parts_group_size(@publication.parts) + 1}\"".html_safe if i == 1 %>>
          <% parts.each do |nav_part| %>
            <% if @publication.current_part == nav_part %>
              <li class="active">
                <span><%= nav_part.title %></span>
              </li>
            <% else %>
              <li>
                <%= link_to nav_part.title, part_path(@publication.slug, nav_part.slug, @edition), :title => "#{ t 'formats.guide.part' } #{ part_number @publication.parts, nav_part }: #{ nav_part.title }" %>
              </li>
            <% end %>
          <% end %>
        </ol>
      <% end %>
    </nav>
  </div>
</aside>
<% end %>

Add span to current guide part
Add span to current guide part

Required now list numbers are displayed
