Trying to map this observation to code and appreciate them starting with very simple examples (that Astra screw-fixed into lean.) But in a simplified way this is close to promting the model to create a set with the members 1,2,1,5 and it correctly creates {1,2,5} in code. So The initial "proof" / instruction was wrong and it silently fixed that. ( Which is one of the failure modes they're describing)