NameError in Kategoris#show

Showing C:/Rails/konkurranceportalen/app/views/kategoris/_rating.html.erb where line #2 raised:

undefined local variable or method `f' for #<#<Class:0x45e97a8>:0x4558ba8>

Extracted source (around line #2):

1: <%= form_tag url_for(controller: 'konkurrancers',  action: 'rate', id: "#{vind.id}"), remote: true %>
2: <%= f.text_field :ratings, :size => 1, :min => 0, :max => 5, :step => 1 %>
3: <div class="rateit" data-rateit-backingfld="#item_ratings" data-rateit-resetable="true">
4: </div>