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diff --git a/predicate-search-core/src/main/java/com/yahoo/search/predicate/optimization/BooleanSimplifier.java b/predicate-search-core/src/main/java/com/yahoo/search/predicate/optimization/BooleanSimplifier.java
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+++ b/predicate-search-core/src/main/java/com/yahoo/search/predicate/optimization/BooleanSimplifier.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.BooleanPredicate;
+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 com.yahoo.document.predicate.PredicateOperator;
+
+import java.util.ArrayList;
+import java.util.List;
+
+/**
+ * Simplifies a predicate by collapsing TRUE/FALSE-children into their parents.
+ * E.g. if an AND node has a FALSE child, the entire node is replaced by FALSE.
+ * Replaces single-child AND/OR-nodes with the child.
+ *
+ * @author magnarn
+ * @author bjorncs
+ */
+public class BooleanSimplifier implements PredicateProcessor {
+
+    public Predicate simplifySubTree(Predicate predicate) {
+        if (predicate == null) {
+            return null;
+        }
+        if (predicate instanceof Conjunction) {
+            List<Predicate> in = ((PredicateOperator)predicate).getOperands();
+            List<Predicate> out = new ArrayList<>(in.size());
+            for (Predicate operand : in) {
+                operand = simplifySubTree(operand);
+                if (isFalse(operand)) {
+                    return new BooleanPredicate(false);
+                } else if (!isTrue(operand)) {
+                    out.add(operand);
+                }
+            }
+            if (out.size() == 1) {
+                return out.get(0);
+            } else if (out.size() == 0) {
+                return new BooleanPredicate(true);
+            }
+            ((Conjunction)predicate).setOperands(out);
+        } else if (predicate instanceof Disjunction) {
+            List<Predicate> in = ((PredicateOperator)predicate).getOperands();
+            List<Predicate> out = new ArrayList<>(in.size());
+            for (Predicate operand : in) {
+                operand = simplifySubTree(operand);
+                if (isTrue(operand)) {
+                    return new BooleanPredicate(true);
+                } else if (!isFalse(operand)) {
+                    out.add(operand);
+                }
+            }
+            if (out.size() == 1) {
+                return out.get(0);
+            } else if (out.size() == 0) {
+                return new BooleanPredicate(false);
+            }
+            ((Disjunction)predicate).setOperands(out);
+        } else if (predicate instanceof Negation) {
+            Predicate operand = ((Negation)predicate).getOperand();
+            operand = simplifySubTree(operand);
+            if (isTrue(operand)) {
+                return new BooleanPredicate(false);
+            } else if (isFalse(operand)) {
+                return new BooleanPredicate(true);
+            }
+            ((Negation) predicate).setOperand(operand);
+        }
+        return predicate;
+    }
+
+    private boolean isFalse(Predicate predicate) {
+        if (predicate instanceof BooleanPredicate) {
+            return !((BooleanPredicate)predicate).getValue();
+        }
+        return false;
+    }
+
+    private boolean isTrue(Predicate predicate) {
+        if (predicate instanceof BooleanPredicate) {
+            return ((BooleanPredicate)predicate).getValue();
+        }
+        return false;
+    }
+
+    @Override
+    public Predicate process(Predicate predicate, PredicateOptions options) {
+        return simplifySubTree(predicate);
+    }
+}