diff --git a/src/FSharp.Data.Adaptive/AdaptifyHelpers.fs b/src/FSharp.Data.Adaptive/AdaptifyHelpers.fs
index 47dc99f..b1244f8 100644
--- a/src/FSharp.Data.Adaptive/AdaptifyHelpers.fs
+++ b/src/FSharp.Data.Adaptive/AdaptifyHelpers.fs
@@ -38,7 +38,7 @@ type ChangeableModelMap<'K, 'V, 'C, 'A>(map : HashMap<'K, 'V>, init : 'V -> 'C,
                     | Remove ->
                         struct (ValueNone, ValueNone)
 
-            let s, ops = HashMap.ApplyDelta(history.State, HashMapDelta.toHashMap ops, apply)
+            let struct(s, ops) = HashMap.ApplyDeltaV(history.State, HashMapDelta.toHashMap ops, apply)
             history.PerformUnsafe(s, HashMapDelta.ofHashMap ops) |> ignore
 
     member x.GetReader() =
diff --git a/src/FSharp.Data.Adaptive/AdaptiveHashSet/AdaptiveHashSet.fs b/src/FSharp.Data.Adaptive/AdaptiveHashSet/AdaptiveHashSet.fs
index 1a9e65b..463a40c 100644
--- a/src/FSharp.Data.Adaptive/AdaptiveHashSet/AdaptiveHashSet.fs
+++ b/src/FSharp.Data.Adaptive/AdaptiveHashSet/AdaptiveHashSet.fs
@@ -652,7 +652,7 @@ module AdaptiveHashSetImplementation =
 
                 struct (outRef, outDelta)
                 
-            let newState, delta = HashMap.ApplyDelta(state, changes, apply)
+            let struct(newState, delta) = HashMap.ApplyDeltaV(state, changes, apply)
             state <- newState
             HashSetDelta.ofHashMap delta
 
@@ -700,7 +700,7 @@ module AdaptiveHashSetImplementation =
 
                 struct (outRef, outDelta)
                 
-            let newState, delta = HashMap.ApplyDelta(state, changes, apply)
+            let struct(newState, delta) = HashMap.ApplyDeltaV(state, changes, apply)
             state <- newState
             HashSetDelta.ofHashMap delta
                   
@@ -748,7 +748,7 @@ module AdaptiveHashSetImplementation =
 
                 struct (outRef, outDelta)
                 
-            let newState, delta = HashMap.ApplyDelta(state, changes, apply)
+            let struct(newState, delta) = HashMap.ApplyDeltaV(state, changes, apply)
             state <- newState
             HashSetDelta.ofHashMap delta
 
diff --git a/src/FSharp.Data.Adaptive/Datastructures/HashCollections.fs b/src/FSharp.Data.Adaptive/Datastructures/HashCollections.fs
index acb6123..ebded78 100644
--- a/src/FSharp.Data.Adaptive/Datastructures/HashCollections.fs
+++ b/src/FSharp.Data.Adaptive/Datastructures/HashCollections.fs
@@ -3846,6 +3846,14 @@ and [<Struct; DebuggerDisplay("Count = {Count}"); DebuggerTypeProxy(typedefof<Ha
         let state = HashMap<'K, 'V>(a.Comparer, state)
         let delta = HashMap<'K, 'U>(a.Comparer, delta)
         state, delta
+
+    [<MethodImpl(MethodImplOptions.AggressiveInlining)>]
+    static member ApplyDeltaV(a : HashMap<'K, 'V>, b : HashMap<'K, 'T>, apply : 'K -> voption<'V> -> 'T -> struct(voption<'V> * voption<'U>)) =
+        let state = a.Root
+        let struct(delta, state) = MapNode.applyDelta a.Comparer (OptimizedClosures.FSharpFunc<_,_,_,_>.Adapt apply) state b.Root
+        let state = HashMap<'K, 'V>(a.Comparer, state)
+        let delta = HashMap<'K, 'U>(a.Comparer, delta)
+        struct(state, delta)
         
     [<MethodImpl(MethodImplOptions.AggressiveInlining)>]
     member x.Choose2V(other : HashMap<'K, 'T>, mapping : 'K -> voption<'V> -> voption<'T> -> voption<'U>) =
diff --git a/src/FSharp.Data.Adaptive/Traceable/CountingHashSet.fs b/src/FSharp.Data.Adaptive/Traceable/CountingHashSet.fs
index a9777b5..071e528 100644
--- a/src/FSharp.Data.Adaptive/Traceable/CountingHashSet.fs
+++ b/src/FSharp.Data.Adaptive/Traceable/CountingHashSet.fs
@@ -45,7 +45,7 @@ type CountingHashSet<'T>(store : HashMap<'T, int>) =
         {
             tmonoid = HashSetDelta.monoid
             tempty = CountingHashSet<'T>(HashMap.empty)
-            tapplyDelta = fun s d -> s.ApplyDeltaNoRefCount d
+            tapplyDelta = fun s d -> s.ApplyDeltaNoRefCountV d
             tcomputeDelta = fun l r -> l.ComputeDelta r
             tprune = None
             tsize = fun s -> s.Count
@@ -213,8 +213,8 @@ type CountingHashSet<'T>(store : HashMap<'T, int>) =
         let mutable res = HashMap<'B, int>.Empty
         for (k,ro) in store do
             let r = mapping k
-            let rr, _ =
-                HashMap<'B, int>.ApplyDelta(res, r.Store, fun _ oldRef delta ->
+            let struct(rr, _) =
+                HashMap<'B, int>.ApplyDeltaV(res, r.Store, fun _ oldRef delta ->
                     let oldRef = match oldRef with | ValueSome o -> o | ValueNone -> 0
                     struct (ValueSome (oldRef + ro * delta), ValueNone)
                 )
@@ -309,7 +309,7 @@ type CountingHashSet<'T>(store : HashMap<'T, int>) =
 
             struct(value, delta)
             
-        let s, d = HashMap.ApplyDelta(store, deltas.Store, apply)
+        let struct(s, d) = HashMap.ApplyDeltaV(store, deltas.Store, apply)
         CountingHashSet s, HashSetDelta d
 
     
@@ -333,9 +333,32 @@ type CountingHashSet<'T>(store : HashMap<'T, int>) =
 
             struct(value, delta)
             
-        let s, d = HashMap.ApplyDelta(store, deltas.Store, apply)
+        let struct(s, d) = HashMap.ApplyDeltaV(store, deltas.Store, apply)
         CountingHashSet s, HashSetDelta d
 
+    /// Integrates the given delta into the set, returns a new set and the effective deltas.
+    member x.ApplyDeltaNoRefCountV (deltas : HashSetDelta<'T>) =
+        let apply (_k : 'T) (o : voption<int>) (d : int) =
+            let o = match o with | ValueSome _ -> 1 | ValueNone -> 0
+            let n = 
+                if d > 0 then 1 
+                elif d < 0 then 0
+                else o
+
+            let delta = 
+                if o = 0 && n > 0 then ValueSome 1
+                elif o > 0 && n = 0 then ValueSome -1
+                else ValueNone
+             
+            let value = 
+                 if n <= 0 then ValueNone
+                 else ValueSome n
+
+            struct(value, delta)
+            
+        let struct(s, d) = HashMap.ApplyDeltaV(store, deltas.Store, apply)
+        struct(CountingHashSet s, HashSetDelta d)
+
     /// Compares two sets.
     static member internal Compare(l : CountingHashSet<'T>, r : CountingHashSet<'T>) =
         let i = l.Intersect r
@@ -511,6 +534,10 @@ module CountingHashSet =
     /// Integrates the given delta into the set without ref-counting, returns a new set and the effective deltas.
     let inline applyDeltaNoRefCount (set : CountingHashSet<'T>) (delta : HashSetDelta<'T>) =
         set.ApplyDeltaNoRefCount delta
+
+    /// Integrates the given delta into the set without ref-counting, returns a new set and the effective deltas.
+    let inline applyDeltaNoRefCountV (set : CountingHashSet<'T>) (delta : HashSetDelta<'T>) =
+        set.ApplyDeltaNoRefCountV delta
         
     /// Compares two sets.
     let internal compare (l : CountingHashSet<'T>) (r : CountingHashSet<'T>) =