What is the difference in meaning between 1 and 2 if "in/within the topic" is modifying "talk"?
1. Let's talk within the topic.
2. Let's talk in the topic.
(2) is hardly understandable. (1) is slightly easier to understand, but to me it does not seem a very natural or usual thing to say. g.
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(2) is hardly understandable. (1) is slightly easier to understand, but to me it does not seem a very natural or usual thing to say. People would say e.g. "Let's stick to the topic".