treat MinProof like Promise before 725438ceae7c, e.g. relevant for performance of session Corec (due to Thm.derivation_closed/close_derivation);
--- a/src/Pure/proofterm.ML Tue Jul 23 19:07:28 2019 +0200
+++ b/src/Pure/proofterm.ML Tue Jul 23 23:10:22 2019 +0200
@@ -394,6 +394,7 @@
| AbsP _ => false
| op % _ => false
| op %% _ => false
+ | MinProof => false
| _ => true);
fun compact_proof (prf % _) = compact_proof prf