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AIMA-Java Core Algorithms from the book Artificial Intelligence a Modern Approach 3rd Ed.
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package aima.core.logic.fol.inference.proof;
import java.util.ArrayList;
import java.util.Collections;
import java.util.List;
import aima.core.logic.fol.kb.data.Chain;
/**
* @author Ciaran O'Reilly
*
*/
public class ProofStepChainContrapositive extends AbstractProofStep {
private List predecessors = new ArrayList();
private Chain contrapositive = null;
private Chain contrapositiveOf = null;
public ProofStepChainContrapositive(Chain contrapositive,
Chain contrapositiveOf) {
this.contrapositive = contrapositive;
this.contrapositiveOf = contrapositiveOf;
this.predecessors.add(contrapositiveOf.getProofStep());
}
//
// START-ProofStep
@Override
public List getPredecessorSteps() {
return Collections.unmodifiableList(predecessors);
}
@Override
public String getProof() {
return contrapositive.toString();
}
@Override
public String getJustification() {
return "Contrapositive: "
+ contrapositiveOf.getProofStep().getStepNumber();
}
// END-ProofStep
//
}