fix: module system: remove WellFounded-specific hacks#9143
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This PR removes a rather ugly hack in the module system, exposing the bodies of theorems whose type mention `WellFounded`. The original motivation was that reducing well-founded definitions (e.g. in `by rfl`) requires reducing proofs, so they need to be available. But reducing proofs is generally fraught with peril, and we have been nudging our users away from using it for a while, e.g. in #5182. Since the module system is opt-in and users will gradually migrate to it, it may be reasonable to expect them to avoid reducing well-founded recursion in the process This way we don't need hacks like this (which, without evidence, I believe would be incomplete anyways) and we get the nice guarantee that within the module system, theorems bodies are always private.
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This PR removes a rather ugly hack in the module system, exposing the bodies of theorems whose type mention
WellFounded.The original motivation was that reducing well-founded definitions (e.g. in
by rfl) requires reducing proofs, so they need to be available.But reducing proofs is generally fraught with peril, and we have been nudging our users away from using it for a while, e.g. in #5182. Since the module system is opt-in and users will gradually migrate to it, it may be reasonable to expect them to avoid reducing well-founded recursion in the process
This way we don't need hacks like this (which, without evidence, I believe would be incomplete anyways) and we get the nice guarantee that within the module system, theorems bodies are always private.