c.a_rev) = c.pull_request.other_ref.split(':') # other_rev is ancestor

        org_scm_instance = c.cs_repo.scm_instance # property with expensive cache invalidation check!!!

        c.cs_repo = c.cs_repo

        c.cs_ranges = [org_scm_instance.get_changeset(x) for x in c.pull_request.revisions]

        c.cs_ranges_org = None # not stored and not important and moving target - could be calculated ...

        revs = [ctx.revision for ctx in reversed(c.cs_ranges)]

        c.jsdata = json.dumps(graph_data(org_scm_instance, revs))

        c.available = []

        c.cs_branch_name = c.cs_ref_name

        other_scm_instance = c.a_repo.scm_instance

        if org_scm_instance.alias == 'hg' and c.a_ref_name != 'ancestor':

            if c.cs_ref_type != 'branch':

                c.cs_branch_name = org_scm_instance.get_changeset(c.cs_ref_name).branch # use ref_type ?

            other_branch_name = c.a_ref_name

            if c.a_ref_type != 'branch':

                other_branch_name = other_scm_instance.get_changeset(c.a_ref_name).branch # use ref_type ?

            # candidates: descendants of old head that are on the right branch

            #             and not are the old head itself ...

            #             and nothing at all if old head is a descendent of target ref name

            if other_scm_instance._repo.revs('present(%s)::&%s', c.cs_ranges[-1].raw_id, other_branch_name):

                c.update_msg = _('This pull request has already been merged to %s.') % other_branch_name

            else: # look for children of PR head on source branch in org repo

                    else:

                        c.update_msg = _('This pull request can be updated with descendent changes on %s:') % c.cs_branch_name

                    c.available = [org_scm_instance.get_changeset(x) for x in arevs]

                else:

                    c.update_msg = _('No changesets found for updating this pull request.')

            revs = org_scm_instance._repo.revs('head() & not (%s::) & branch(%s) & !closed()', revs[0], c.cs_branch_name)

            if revs:

                c.update_msg_other = _('Note: Branch %s also contains unrelated changes, such as %s.') % (c.cs_branch_name,

                    h.short_id(org_scm_instance.get_changeset((max(revs))).raw_id))

            else:

                c.update_msg_other = _('Branch %s does not contain other changes.') % c.cs_branch_name

        raw_ids = [x.raw_id for x in c.cs_ranges]

        c.cs_comments = c.cs_repo.get_comments(raw_ids)

        c.statuses = c.cs_repo.statuses(raw_ids)

        ignore_whitespace = request.GET.get('ignorews') == '1'

        line_context = request.GET.get('context', 3)

        c.ignorews_url = _ignorews_url

        c.context_url = _context_url

        c.fulldiff = request.GET.get('fulldiff')

        diff_limit = self.cut_off_limit if not c.fulldiff else None

                %endif

              %endif

              ## TODO: this check feels wrong, it would be better to have a check for permissions

              ## also it feels like a job for the controller

              %if c.authuser.username != 'default':

                  <li>

                   <a class="${follow_class()}" onclick="javascript:toggleFollowingRepo(this,${c.db_repo.repo_id},'${str(h.get_token())}');">

                    <span class="show-follow"><i class="icon-heart-empty"></i> ${_('Follow')}</span>

                    <span class="show-following"><i class="icon-heart"></i> ${_('Unfollow')}</span>

                  </a>

                  </li>

                  <li><a href="${h.url('repo_fork_home',repo_name=c.repo_name)}"><i class="icon-code-fork"></i> ${_('Fork')}</a></li>

                  <li><a href="${h.url('pullrequest_home',repo_name=c.repo_name)}"><i class="icon-code-fork"></i> ${_('Create Pull Request')}</a></li>

              %endif

             </ul>

        </li>

        <li ${is_current('showpullrequest')}>

          <a href="${h.url('pullrequest_show_all',repo_name=c.repo_name)}" title="${_('Show Pull Requests for %s') % c.repo_name}"> <i class="icon-code-fork"></i> ${_('Pull Requests')}

            %if c.repository_pull_requests:

              <span>${c.repository_pull_requests}</span>

            %endif

          </a>

        </li>

      </ul>

  </div>