Show thread number in the post number if post has many threads

boards/models/post.py

@@ -443,3 +443,9 b' class Post(models.Model, Viewable):'
 
     def get_raw_text(self) -> str:
         return self.text
+
+    def get_absolute_id(self) -> str:
+        if self.get_threads().count() > 1:
+            return '{}/{}'.format(self.get_thread().get_opening_post_id(), self.id)
+        else:
+            return str(self.id)

boards/templates/boards/post.html

@@ -16,7 +16,7 b''
     <a class="post_id" href="{% post_object_url post thread=thread %}"
             {% if not truncated and not thread.archived %}
        onclick="javascript:addQuickReply('{{ post.id }}'); return false;"
-       title="{% trans 'Quote' %}" {% endif %}>({{ post.id }})</a>
+       title="{% trans 'Quote' %}" {% endif %}>({{ post.get_absolute_id }})</a>
     <span class="title">{{ post.title }}</span>
     <span class="pub_time">{{ post.pub_time }}</span>
     {% comment %}