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diff --git a/subprojects/viatra-runtime-rete/src/main/java/tools/refinery/viatra/runtime/rete/network/mailbox/timeless/AbstractUpdateSplittingMailbox.java b/subprojects/viatra-runtime-rete/src/main/java/tools/refinery/viatra/runtime/rete/network/mailbox/timeless/AbstractUpdateSplittingMailbox.java
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+++ b/subprojects/viatra-runtime-rete/src/main/java/tools/refinery/viatra/runtime/rete/network/mailbox/timeless/AbstractUpdateSplittingMailbox.java
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+/*******************************************************************************
+ * Copyright (c) 2010-2018, Tamas Szabo, Istvan Rath and Daniel Varro
+ * This program and the accompanying materials are made available under the
+ * terms of the Eclipse Public License v. 2.0 which is available at
+ * http://www.eclipse.org/legal/epl-v20.html.
+ * 
+ * SPDX-License-Identifier: EPL-2.0
+ *******************************************************************************/
+package tools.refinery.viatra.runtime.rete.network.mailbox.timeless;
+
+import tools.refinery.viatra.runtime.rete.network.Receiver;
+import tools.refinery.viatra.runtime.rete.network.ReteContainer;
+import tools.refinery.viatra.runtime.rete.network.communication.CommunicationGroup;
+import tools.refinery.viatra.runtime.rete.network.indexer.MessageIndexer;
+import tools.refinery.viatra.runtime.rete.network.mailbox.Mailbox;
+import tools.refinery.viatra.runtime.rete.network.mailbox.MessageIndexerFactory;
+
+/**
+ * An abstract mailbox implementation that is capable of splitting update messages based on some form of monotonicity
+ * (anti-monotone and monotone). The monotonicity is either defined by the less or equal operator of a poset or, it can
+ * be the standard subset ordering among sets of tuples.
+ * 
+ * @author Tamas Szabo
+ * @since 2.0
+ *
+ */
+public abstract class AbstractUpdateSplittingMailbox<IndexerType extends MessageIndexer, ReceiverType extends Receiver> implements Mailbox {
+
+    protected IndexerType monotoneQueue;
+    protected IndexerType antiMonotoneQueue;
+    protected IndexerType monotoneBuffer;
+    protected IndexerType antiMonotoneBuffer;
+    protected boolean deliveringMonotone;
+    protected boolean deliveringAntiMonotone;
+    protected final ReceiverType receiver;
+    protected final ReteContainer container;
+    protected CommunicationGroup group;
+
+    public AbstractUpdateSplittingMailbox(final ReceiverType receiver, final ReteContainer container,
+            final MessageIndexerFactory<IndexerType> factory) {
+        this.receiver = receiver;
+        this.container = container;
+        this.monotoneQueue = factory.create();
+        this.antiMonotoneQueue = factory.create();
+        this.monotoneBuffer = factory.create();
+        this.antiMonotoneBuffer = factory.create();
+        this.deliveringMonotone = false;
+        this.deliveringAntiMonotone = false;
+    }
+
+    protected void swapAndClearMonotone() {
+        final IndexerType tmp = this.monotoneQueue;
+        this.monotoneQueue = this.monotoneBuffer;
+        this.monotoneBuffer = tmp;
+        this.monotoneBuffer.clear();
+    }
+
+    protected void swapAndClearAntiMonotone() {
+        final IndexerType tmp = this.antiMonotoneQueue;
+        this.antiMonotoneQueue = this.antiMonotoneBuffer;
+        this.antiMonotoneBuffer = tmp;
+        this.antiMonotoneBuffer.clear();
+    }
+
+    protected IndexerType getActiveMonotoneQueue() {
+        if (this.deliveringMonotone) {
+            return this.monotoneBuffer;
+        } else {
+            return this.monotoneQueue;
+        }
+    }
+
+    protected IndexerType getActiveAntiMonotoneQueue() {
+        if (this.deliveringAntiMonotone) {
+            return this.antiMonotoneBuffer;
+        } else {
+            return this.antiMonotoneQueue;
+        }
+    }
+
+    @Override
+    public ReceiverType getReceiver() {
+        return this.receiver;
+    }
+
+    @Override
+    public void clear() {
+        this.monotoneQueue.clear();
+        this.antiMonotoneQueue.clear();
+        this.monotoneBuffer.clear();
+        this.antiMonotoneBuffer.clear();
+    }
+
+    @Override
+    public boolean isEmpty() {
+        return this.getActiveMonotoneQueue().isEmpty() && this.getActiveAntiMonotoneQueue().isEmpty();
+    }
+
+    @Override
+    public CommunicationGroup getCurrentGroup() {
+        return this.group;
+    }
+
+    @Override
+    public void setCurrentGroup(final CommunicationGroup group) {
+        this.group = group;
+    }
+    
+}