org.logicng.transformations.qe.UniversalQuantifierElimination Maven / Gradle / Ivy
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// The Next Generation Logic Library //
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// Copyright 2015-20xx Christoph Zengler //
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// Licensed under the Apache License, Version 2.0 (the "License"); //
// you may not use this file except in compliance with the License. //
// You may obtain a copy of the License at //
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// http://www.apache.org/licenses/LICENSE-2.0 //
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// Unless required by applicable law or agreed to in writing, software //
// distributed under the License is distributed on an "AS IS" BASIS, //
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// permissions and limitations under the License. //
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package org.logicng.transformations.qe;
import org.logicng.datastructures.Assignment;
import org.logicng.formulas.Formula;
import org.logicng.formulas.FormulaFactory;
import org.logicng.formulas.FormulaTransformation;
import org.logicng.formulas.Variable;
import java.util.Arrays;
import java.util.Collection;
/**
* This transformation eliminates a number of universally quantified variables by replacing them with the Shannon
* expansion. If {@code x} is eliminated from a formula {@code f}, the resulting formula is
* {@code f[true/x] & f[false/x]}.
*
* This transformation cannot be cached since it is dependent on the set of literals to eliminate.
* @version 1.0
* @since 1.0
*/
public final class UniversalQuantifierElimination implements FormulaTransformation {
private final Variable[] elimination;
/**
* Constructs a new universal quantifier elimination for the given variables.
* @param variables the variables
*/
public UniversalQuantifierElimination(final Variable... variables) {
this.elimination = Arrays.copyOf(variables, variables.length);
}
/**
* Constructs a new universal quantifier elimination for a given collection of variables.
* @param variables the collection of variables
*/
public UniversalQuantifierElimination(final Collection variables) {
this.elimination = variables.toArray(new Variable[0]);
}
@Override
public Formula apply(final Formula formula, final boolean cache) {
Formula result = formula;
final FormulaFactory f = formula.factory();
for (final Variable var : this.elimination) {
result = f.and(result.restrict(new Assignment(var)), result.restrict(new Assignment(var.negate())));
}
return result;
}
}