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diff --git a/predicate-search-core/src/main/java/com/yahoo/search/predicate/optimization/AndOrSimplifier.java b/predicate-search-core/src/main/java/com/yahoo/search/predicate/optimization/AndOrSimplifier.java
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+++ b/predicate-search-core/src/main/java/com/yahoo/search/predicate/optimization/AndOrSimplifier.java
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+// Copyright 2016 Yahoo Inc. Licensed under the terms of the Apache 2.0 license. See LICENSE in the project root.
+package com.yahoo.search.predicate.optimization;
+
+import com.yahoo.document.predicate.Conjunction;
+import com.yahoo.document.predicate.Disjunction;
+import com.yahoo.document.predicate.Negation;
+import com.yahoo.document.predicate.Predicate;
+
+import java.util.ArrayList;
+import java.util.List;
+
+/**
+ * Simplifies a predicate by:
+ *  - Combining child-AND/OR nodes with direct parents of the same type
+ *  - Pushing negations down to leaf nodes by using De Morgan's law.
+ *
+ * @author magnarn
+ * @author bjorncs
+ */
+public class AndOrSimplifier implements PredicateProcessor {
+
+    public Predicate simplifySubTree(Predicate predicate, boolean negated) {
+        if (predicate == null) {
+            return null;
+        }
+        if (predicate instanceof Negation) {
+            return simplifySubTree(((Negation) predicate).getOperand(), !negated);
+        } else if (predicate instanceof Conjunction) {
+            List<Predicate> in = ((Conjunction)predicate).getOperands();
+            List<Predicate> out = new ArrayList<>(in.size());
+            for (Predicate operand : in) {
+                operand = simplifySubTree(operand, negated);
+                if (operand instanceof Conjunction) {
+                    out.addAll(((Conjunction)operand).getOperands());
+                } else {
+                    out.add(operand);
+                }
+            }
+            if (negated) {
+                return new Disjunction(out);
+            }
+            ((Conjunction)predicate).setOperands(out);
+        } else if (predicate instanceof Disjunction) {
+            List<Predicate> in = ((Disjunction)predicate).getOperands();
+            List<Predicate> out = new ArrayList<>(in.size());
+            for (Predicate operand : in) {
+                operand = simplifySubTree(operand, negated);
+                if (operand instanceof Disjunction) {
+                    out.addAll(((Disjunction)operand).getOperands());
+                } else {
+                    out.add(operand);
+                }
+            }
+            if (negated) {
+                return new Conjunction(out);
+            }
+            ((Disjunction)predicate).setOperands(out);
+        } else {
+            if (negated) {
+                return new Negation(predicate);
+            }
+        }
+        return predicate;
+    }
+
+    @Override
+    public Predicate process(Predicate predicate, PredicateOptions options) {
+        return simplifySubTree(predicate, false);
+    }
+}