Extrinsic termination proofs for well-founded recursion in Lean

A few months ago I explained that one reason why this blog has become more quiet is that all my work on Lean is covered elsewhere. This post is an exception, because it is an observation that is (arguably) interesting, but does not lead anywhere, so where else to put it than my own blog… Want to share your thoughts about this? Please join the discussion on the Lean community zulip ! Background…