mkCongrSimpCore?
This PR fixes another issue at the `congr_simp` theorems that was affecting Mathlib. Many thanks to Johan Commelin for creating the mwe. closes #9466
This PR fixes a bug at `mkCongrSimpCore?`. It fixes the issue reported by @joehendrix at #9388. The fix is just commit: afc4ba617fe2ca5828e0e252558d893d7791d56b. The rest of the PR is just cleaning up the file. closes #9388