anchor.diff:  <div class="radio">
     <label>
       <input name="assignment[teamset_plan]" id="teamset_new" type="radio"
  -           value="new" <% if @legal_actions[:new][:checked] %>checked<% end %>>
  +           value="new" <% if asgn.teamset_plan == "new" || @legal_actions[:new][:checked] %>checked<% end %>>
       <strong>New teamset:</strong> after creating this assignment, go to the Teams
       page to create a new set of teams.
       <% if @legal_actions[:new][:existing] %>
  
positive.code: <div class="radio">
    <label>
      <input name="assignment[teamset_plan]" id="teamset_none" type="radio"
             value="none" <% if @legal_actions[:no_teams][:checked] %>checked<% end %>>
      <strong>No teams:</strong> this assignment will be submitted individually
    </label>
  </div>
  
negative.code:     will be ignored.
      <br>
      <%= select_tag "assignment[teamset_source_copy]",
          options_from_collection_for_select(course.teamsets, "id", "name", asgn.teamset_source_copy&.to_i),
          prompt: [asgn.teamset_source_copy,
                   "Choose an existing teamset"].find(&:presence),
          class: "col-sm-12" %>
    </label>
  </div>
  