.

wcfs/internal/xbtree/pptreesubset.go

@@ -141,7 +141,7 @@ func (S PPTreeSubSet) AddPath(path []zodb.Oid) {
 
 // Union returns U = PP(A.leafs | B.leafs)
 //
-// In other words it returns sum of A and B.
+// In other words it adds A and B nodes.
 func (A PPTreeSubSet) Union(B PPTreeSubSet) PPTreeSubSet {
 	U := A.Clone()
 	U.UnionInplace(B)
@@ -168,7 +168,7 @@ func (A PPTreeSubSet) UnionInplace(B PPTreeSubSet) {
 
 // Difference returns D = PP(A.leafs \ B.leafs)
 //
-// In other words ... XXX
+// In other words it removes B nodes from A while still maintaining A as PP-connected.
 func (A PPTreeSubSet) Difference(B PPTreeSubSet) PPTreeSubSet {
 	D := A.Clone()
 	D.DifferenceInplace(B)

wcfs/internal/xbtree/δbtail.go

@@ -251,9 +251,12 @@ func (δBtail *ΔBtail) track(key Key, path []zodb.Oid) error {
 
 	root := path[0]
 
+	// XXX first normalize path
+
 	// nothing to do if key is already tracked
 	leaf := path[len(path)-1]
 	if δBtail.trackSet.Has(leaf) {
+		tracefΔBtail("->T: nop\n")
 		path_ := δBtail.trackSet.Path(leaf)
 		if !pathEqual(path, path_) {
 			panicf("BUG: key %s is already tracked via path=%v\ntrack requests path=%v",  kstr(key), path_, path)
@@ -270,6 +273,7 @@ func (δBtail *ΔBtail) track(key Key, path []zodb.Oid) error {
 
 	δBtail.trackNewRoots.Add(root)
 	δTtail.trackNew.AddPath(path)
+	tracefΔBtail("->T: [%s].trackNew -> %s\n", root, δTtail.trackNew)
 	return nil
 }