old_contents: from .. import models
  from django import template
  
  register = template.Library()
  
  
  @register.filter
  def is_member(gestalt, group):
      return models.Membership.objects.filter(
              gestalt=gestalt, group=group).exists()
  
new_contents: from .. import models
  from django import template
  
  register = template.Library()
  
  
  @register.filter
  def is_member(gestalt, group):
      return models.Membership.objects.filter(
              group=group, member=gestalt).exists()
  
subject: Fix templatetag