old_contents: from django.conf.urls import url
  from . import views
  
  
  handler404 = 'main.views.page_not_found_view'
  handler500 = 'main.views.error_view'
  handler403 = 'main.views.permission_denied_view'
  handler400 = 'main.views.bad_request_view'
  
  urlpatterns = [
      url(r'^tutorial/', views.tutorial, name='tutorial'),
      url(r'^introduction/', views.introduction, name='introduction'),
  ]
  
new_contents: from django.conf.urls import url
  from . import views
  
  
  handler404 = 'main.views.page_not_found_view'
  handler500 = 'main.views.error_view'
  handler403 = 'main.views.permission_denied_view'
  handler400 = 'main.views.bad_request_view'
  
  urlpatterns = [
      url(r'^tutorial/', views.tutorial, name='tutorial'),
      url(r'^$', views.introduction, name='introduction'),
  ]
  
subject: change url 'introduction'