The README in nbtree mentions that L&Y algorithm must couple locks when moving right during ascent for insertion. However, it's hard to see why that's necessary. Since L&Y mostly discussed concurrent insertions and searches, what can go wrong if inserters only acquire one lock at a time?
The Lanin&ShaSha paper cited in README also agrees that B-link structure allows inserts and searches to lock only one node at a time although it's not apparent in L&Y itself.
