diff --git a/src/Builtin/Subjects.cs b/src/Builtin/Subjects.cs
new file mode 100644
index 0000000..fbf8462
--- /dev/null
+++ b/src/Builtin/Subjects.cs
@@ -0,0 +1,228 @@
+namespace DCFApixels.DragonECS
+{
+    public class SingleSubject<TComponent, TPool> : EcsSubject where TPool : IEcsPoolImplementation<TComponent>, new()
+    {
+        public readonly TPool pool;
+        public SingleSubject(Builder b)
+        {
+            pool = b.Include<TComponent, TPool>();
+        }
+    }
+    public class CombinedSubject<S0, S1> : EcsSubject
+        where S0 : EcsSubject
+        where S1 : EcsSubject
+    {
+        public readonly S0 s0;
+        public readonly S1 s1;
+        public CombinedSubject(Builder b)
+        {
+            s0 = b.Combine<S0>();
+            s1 = b.Combine<S1>();
+        }
+    }
+
+    public class CombinedSubject<S0, S1, S2> : EcsSubject
+        where S0 : EcsSubject
+        where S1 : EcsSubject
+        where S2 : EcsSubject
+    {
+        public readonly S0 s0;
+        public readonly S1 s1;
+        public readonly S2 s2;
+        public CombinedSubject(Builder b)
+        {
+            s0 = b.Combine<S0>();
+            s1 = b.Combine<S1>();
+            s2 = b.Combine<S2>();
+        }
+    }
+
+    public class CombinedSubject<S0, S1, S2, S3> : EcsSubject
+        where S0 : EcsSubject
+        where S1 : EcsSubject
+        where S2 : EcsSubject
+        where S3 : EcsSubject
+    {
+        public readonly S0 s0;
+        public readonly S1 s1;
+        public readonly S2 s2;
+        public readonly S3 s3;
+        public CombinedSubject(Builder b)
+        {
+            s0 = b.Combine<S0>();
+            s1 = b.Combine<S1>();
+            s2 = b.Combine<S2>();
+            s3 = b.Combine<S3>();
+        }
+    }
+
+    public class CombinedSubject<S0, S1, S2, S3, S4> : EcsSubject
+        where S0 : EcsSubject
+        where S1 : EcsSubject
+        where S2 : EcsSubject
+        where S3 : EcsSubject
+        where S4 : EcsSubject
+    {
+        public readonly S0 s0;
+        public readonly S1 s1;
+        public readonly S2 s2;
+        public readonly S3 s3;
+        public readonly S4 s4;
+        public CombinedSubject(Builder b)
+        {
+            s0 = b.Combine<S0>();
+            s1 = b.Combine<S1>();
+            s2 = b.Combine<S2>();
+            s3 = b.Combine<S3>();
+            s4 = b.Combine<S4>();
+        }
+    }
+
+    public class CombinedSubject<S0, S1, S2, S3, S4, S5> : EcsSubject
+        where S0 : EcsSubject
+        where S1 : EcsSubject
+        where S2 : EcsSubject
+        where S3 : EcsSubject
+        where S4 : EcsSubject
+        where S5 : EcsSubject
+    {
+        public readonly S0 s0;
+        public readonly S1 s1;
+        public readonly S2 s2;
+        public readonly S3 s3;
+        public readonly S4 s4;
+        public readonly S5 s5;
+        public CombinedSubject(Builder b)
+        {
+            s0 = b.Combine<S0>();
+            s1 = b.Combine<S1>();
+            s2 = b.Combine<S2>();
+            s3 = b.Combine<S3>();
+            s4 = b.Combine<S4>();
+            s5 = b.Combine<S5>();
+        }
+    }
+
+    public static class CombinedSubjectExtensions
+    {
+        #region 2
+        public static EcsReadonlyGroup Where<S0, S1>(this EcsWorld self, out S0 s0, out S1 s1)
+            where S0 : EcsSubject
+            where S1 : EcsSubject
+        {
+            return self.WhereFor(self.Entities, out s0, out s1);
+        }
+        public static EcsReadonlyGroup WhereFor<S0, S1>(this EcsWorld self, EcsReadonlyGroup sourceGroup, out S0 s0, out S1 s1)
+            where S0 : EcsSubject
+            where S1 : EcsSubject
+        {
+            var combined = self.GetSubject<CombinedSubject<S0, S1>>();
+            s0 = combined.s0;
+            s1 = combined.s1;
+            return self.WhereFor<CombinedSubject<S0, S1>>(sourceGroup);
+        }
+        #endregion
+
+        #region 3
+        public static EcsReadonlyGroup Where<S0, S1, S2>(this EcsWorld self, out S0 s0, out S1 s1, out S2 s2)
+            where S0 : EcsSubject
+            where S1 : EcsSubject
+            where S2 : EcsSubject
+        {
+            return self.WhereFor(self.Entities, out s0, out s1, out s2);
+        }
+        public static EcsReadonlyGroup WhereFor<S0, S1, S2>(this EcsWorld self, EcsReadonlyGroup sourceGroup, out S0 s0, out S1 s1, out S2 s2)
+            where S0 : EcsSubject
+            where S1 : EcsSubject
+            where S2 : EcsSubject
+        {
+            var combined = self.GetSubject<CombinedSubject<S0, S1, S2>>();
+            s0 = combined.s0;
+            s1 = combined.s1;
+            s2 = combined.s2;
+            return self.WhereFor<CombinedSubject<S0, S1, S2>>(sourceGroup);
+        }
+        #endregion
+
+        #region 4
+        public static EcsReadonlyGroup Where<S0, S1, S2, S3>(this EcsWorld self, out S0 s0, out S1 s1, out S2 s2, out S3 s3)
+            where S0 : EcsSubject
+            where S1 : EcsSubject
+            where S2 : EcsSubject
+            where S3 : EcsSubject
+        {
+            return self.WhereFor(self.Entities, out s0, out s1, out s2, out s3);
+        }
+        public static EcsReadonlyGroup WhereFor<S0, S1, S2, S3>(this EcsWorld self, EcsReadonlyGroup sourceGroup, out S0 s0, out S1 s1, out S2 s2, out S3 s3)
+            where S0 : EcsSubject
+            where S1 : EcsSubject
+            where S2 : EcsSubject
+            where S3 : EcsSubject
+        {
+            var combined = self.GetSubject<CombinedSubject<S0, S1, S2, S3>>();
+            s0 = combined.s0;
+            s1 = combined.s1;
+            s2 = combined.s2;
+            s3 = combined.s3;
+            return self.WhereFor<CombinedSubject<S0, S1, S2, S3>>(sourceGroup);
+        }
+        #endregion
+
+        #region 5
+        public static EcsReadonlyGroup Where<S0, S1, S2, S3, S4>(this EcsWorld self, out S0 s0, out S1 s1, out S2 s2, out S3 s3, out S4 s4)
+            where S0 : EcsSubject
+            where S1 : EcsSubject
+            where S2 : EcsSubject
+            where S3 : EcsSubject
+            where S4 : EcsSubject
+        {
+            return self.WhereFor(self.Entities, out s0, out s1, out s2, out s3, out s4);
+        }
+        public static EcsReadonlyGroup WhereFor<S0, S1, S2, S3, S4>(this EcsWorld self, EcsReadonlyGroup sourceGroup, out S0 s0, out S1 s1, out S2 s2, out S3 s3, out S4 s4)
+            where S0 : EcsSubject
+            where S1 : EcsSubject
+            where S2 : EcsSubject
+            where S3 : EcsSubject
+            where S4 : EcsSubject
+        {
+            var combined = self.GetSubject<CombinedSubject<S0, S1, S2, S3, S4>>();
+            s0 = combined.s0;
+            s1 = combined.s1;
+            s2 = combined.s2;
+            s3 = combined.s3;
+            s4 = combined.s4;
+            return self.WhereFor<CombinedSubject<S0, S1, S2, S3, S4>>(sourceGroup);
+        }
+        #endregion
+
+        #region 6
+        public static EcsReadonlyGroup Where<S0, S1, S2, S3, S4, S5>(this EcsWorld self, out S0 s0, out S1 s1, out S2 s2, out S3 s3, out S4 s4, out S5 s5)
+            where S0 : EcsSubject
+            where S1 : EcsSubject
+            where S2 : EcsSubject
+            where S3 : EcsSubject
+            where S4 : EcsSubject
+            where S5 : EcsSubject
+        {
+            return self.WhereFor(self.Entities, out s0, out s1, out s2, out s3, out s4, out s5);
+        }
+        public static EcsReadonlyGroup WhereFor<S0, S1, S2, S3, S4, S5>(this EcsWorld self, EcsReadonlyGroup sourceGroup, out S0 s0, out S1 s1, out S2 s2, out S3 s3, out S4 s4, out S5 s5)
+            where S0 : EcsSubject
+            where S1 : EcsSubject
+            where S2 : EcsSubject
+            where S3 : EcsSubject
+            where S4 : EcsSubject
+            where S5 : EcsSubject
+        {
+            var combined = self.GetSubject<CombinedSubject<S0, S1, S2, S3, S4, S5>>();
+            s0 = combined.s0;
+            s1 = combined.s1;
+            s2 = combined.s2;
+            s3 = combined.s3;
+            s4 = combined.s4;
+            s5 = combined.s5;
+            return self.WhereFor<CombinedSubject<S0, S1, S2, S3, S4, S5>>(sourceGroup);
+        }
+        #endregion
+    }
+}
diff --git a/src/EcsSubject.cs b/src/EcsSubject.cs
index 0da9ce9..9fbfbf0 100644
--- a/src/EcsSubject.cs
+++ b/src/EcsSubject.cs
@@ -35,22 +35,22 @@ namespace DCFApixels.DragonECS
         public sealed class Builder : EcsSubjectBuilderBase
         {
             private EcsWorld _world;
-            private List<int> _inc;
-            private List<int> _exc;
+            private HashSet<int> _inc;
+            private HashSet<int> _exc;
 
             public EcsWorld World => _world;
 
             private Builder(EcsWorld world)
             {
                 _world = world;
-                _inc = new List<int>(8);
-                _exc = new List<int>(4);
+                _inc = new HashSet<int>(8);
+                _exc = new HashSet<int>(4);
             }
             internal static TSubject Build<TSubject>(EcsWorld world) where TSubject : EcsSubject
             {
                 Builder builder = new Builder(world);
-                Type queryType = typeof(TSubject);
-                ConstructorInfo constructorInfo = queryType.GetConstructor(BindingFlags.Instance | BindingFlags.Public | BindingFlags.NonPublic, null, new Type[] { typeof(Builder) }, null);
+                Type subjectType = typeof(TSubject);
+                ConstructorInfo constructorInfo = subjectType.GetConstructor(BindingFlags.Instance | BindingFlags.Public | BindingFlags.NonPublic, null, new Type[] { typeof(Builder) }, null);
                 EcsSubject newSubject;
                 if (constructorInfo != null)
                 {
@@ -100,11 +100,24 @@ namespace DCFApixels.DragonECS
             }
             #endregion
 
+            #region Combine
+            public TOtherSubject Combine<TOtherSubject>() where TOtherSubject : EcsSubject
+            {
+                var result = _world.GetSubject<TOtherSubject>();
+                _inc.UnionWith(result.mask._inc);
+                _exc.UnionWith(result.mask._exc);
+                return result;
+            }
+            #endregion
+
             private void End(out EcsMask mask)
             {
-                _inc.Sort();
-                _exc.Sort();
-                mask = new EcsMask(_world.Archetype, _inc.ToArray(), _exc.ToArray());
+                var inc = _inc.ToArray();
+                Array.Sort(inc);
+                var exc = _exc.ToArray();
+                Array.Sort(exc);
+
+                mask = new EcsMask(_world.Archetype, inc, exc);
                 _world = null;
                 _inc = null;
                 _exc = null;
@@ -161,12 +174,25 @@ namespace DCFApixels.DragonECS
             _exc = exc;
         }
 
+        public static EcsMask Union(EcsMask a, EcsMask b)
+        {
+            if(a._worldType != b._worldType) ThrowHelper.ThrowArgumentDifferentWorldsException();
+
+            HashSet<int> incset = new HashSet<int>(a._inc);
+            HashSet<int> excset = new HashSet<int>(a._exc);
+            incset.UnionWith(b._inc);
+            excset.UnionWith(b._exc);
+            return new EcsMask(a._worldType, incset.ToArray(), excset.ToArray());
+        }   
+
+        #region Object
         public override string ToString() => CreateLogString(_worldType, _inc, _exc);
+        #endregion
 
         #region Debug utils
         private static string CreateLogString(Type worldType, int[] inc, int[] exc)
         {
-#if DEBUG
+#if (DEBUG && !DISABLE_DEBUG)
             int worldID = WorldMetaStorage.GetWorldID(worldType);
             string converter(int o) => EcsDebugUtility.GetGenericTypeName(WorldMetaStorage.GetComponentType(worldID, o), 1);
             return $"Inc({string.Join(", ", inc.Select(converter))}) Exc({string.Join(", ", exc.Select(converter))})";
@@ -194,6 +220,14 @@ namespace DCFApixels.DragonECS
             public override string ToString() => CreateLogString(worldType, inc, exc);
         }
         #endregion
+
+        #region ThrowHelper
+        internal static class ThrowHelper
+        {
+            [MethodImpl(MethodImplOptions.NoInlining)]
+            public static void ThrowArgumentDifferentWorldsException() => throw new ArgumentException("The groups belong to different worlds.");
+        }
+        #endregion
     }
     #endregion