> For instance if you wrote a type to extend number to something like range<min,max> - obviously a toy - it would look very similar to what you’ve posted. Why

> For instance if you wrote a type to extend number to something like range<min,max> - obviously a toy - it would look very similar to what you’ve posted. Why would Range need a sentinel? My point is that using a sentinel to bridge TypeScript's lack of generic arity-based specialization is a non-trivial problem. After you mentioned it, I looked for examples on Google and couldn't find anything that matches precisely. I'm not claiming humans can't solve this, or that gpt5 invented something fundamentally new. My original point was about productivity at scale. Having a model apply the right solution across dozens of similar problems, rather than me manually figuring out each one.