RE: Difference between required topic and exclusive topic

You can clear the topic using the Self code "conversation.topic = null" either from a Template or a think block.

You can set the initial topic in a greeting.

greeting: Welcome, lets talk about sports.
topic: sports

clear the topic
template: Okay, I was getting tired of talking about {conversation.topic} anyway. {think(conversation.topic=null)}
condition: conversation.topic != null

clear the topic 2
Okay, I was getting tired of talking about it anyway.
think: conversation.topic = null;