.

wcfs/δbtail.go

@@ -957,7 +957,7 @@ func (rs rangeSplit) Get_(k Key) (rnode *nodeInRange, ok bool) {
 // rnode.node must be tree.
 // rnode.node must be already activated.
 //
-// inserted children is also returned for convenience.
+// inserted children are returned for convenience.
 func (prs *rangeSplit) Expand(rnode *nodeInRange) (children rangeSplit) {
 	rs := *prs
 	i := sort.Search(len(rs), func(i int) bool {

wcfs/δbtail_test.go

@@ -546,6 +546,10 @@ func xzgetBlkDataAt(db *zodb.DB, zblkOid zodb.Oid, at zodb.Tid) string {
 //
 // i.e. = δ(Av, Bv) for k: k ∈ U kadj(A,B)[·]
 //                            ·∈T
+//
+// XXX adjacency matrix is symmetric:	XXX KAdj verifies this at runtime
+//
+//	kadj(A,B) == kadj(B,A)
 type KAdjMatrix map[Key]SetKey
 
 // Map returns kadj·keys .
@@ -568,6 +572,17 @@ func (kadj KAdjMatrix) Map(keys SetKey) SetKey {
 //
 // KAdj itself is verified by testΔBTail on entries with .kadjOK set.
 func KAdj(t1, t2 *tTreeCommit, keysv ...SetKey) (kadj KAdjMatrix) {
+	// XXX vvv verifies that KAdj(A,B) == KAdj(B,A)
+	kadj12 := _KAdj(t1,t2, keysv...)
+	kadj21 := _KAdj(t2,t1, keysv...)
+	if !reflect.DeepEqual(kadj12, kadj21) {
+		panicf("KAdj not symmetric:\nt1: %s\bt2: %s\nkadj12: %v\nkadj21: %v",
+			t1.tree, t2.tree, kadj12, kadj21)
+	}
+	return kadj12
+}
+
+func _KAdj(t1, t2 *tTreeCommit, keysv ...SetKey) (kadj KAdjMatrix) {
 	var keys SetKey
 	switch len(keysv) {
 	case 0: