code: package it.unibz.inf.ontop.model.term.functionsymbol.impl;
  
  import com.google.common.collect.ImmutableList;
  import it.unibz.inf.ontop.iq.node.VariableNullability;
  import it.unibz.inf.ontop.model.term.Constant;
  import it.unibz.inf.ontop.model.term.ImmutableTerm;
  import it.unibz.inf.ontop.model.term.TermFactory;
  import it.unibz.inf.ontop.model.type.*;
  import it.unibz.inf.ontop.utils.ImmutableCollectors;
  import org.apache.commons.rdf.api.IRI;
  
  import javax.annotation.Nonnull;
  import java.util.Optional;
  
  
  public abstract class AbstractBinaryComparisonSPARQLFunctionSymbol extends SPARQLFunctionSymbolImpl {
  
      private final RDFDatatype xsdBooleanType;
  
      protected AbstractBinaryComparisonSPARQLFunctionSymbol(@Nonnull String functionSymbolName, @Nonnull IRI functionIRI,
                                                             @Nonnull RDFTermType rdfRootType, RDFDatatype xsdBooleanType) {
          super(functionSymbolName, functionIRI, ImmutableList.of(rdfRootType, rdfRootType));
          this.xsdBooleanType = xsdBooleanType;
      }
  
      protected AbstractBinaryComparisonSPARQLFunctionSymbol(@Nonnull String functionSymbolName, @Nonnull String officialName,
                                                             @Nonnull RDFTermType rdfRootType, RDFDatatype xsdBooleanType) {
          super(functionSymbolName, officialName, ImmutableList.of(rdfRootType, rdfRootType));
          this.xsdBooleanType = xsdBooleanType;
      }
  
      @Override
      protected boolean tolerateNulls() {
          return false;
      }
  
      @Override
      public boolean isAlwaysInjectiveInTheAbsenceOfNonInjectiveFunctionalTerms() {
          return false;
      }
  
      @Override
      public Optional<TermTypeInference> inferType(ImmutableList<? extends ImmutableTerm> terms) {
          return Optional.of(TermTypeInference.declareTermType(xsdBooleanType));
      }
  
      @Override
      public boolean canBePostProcessed(ImmutableList<? extends ImmutableTerm> arguments) {
          return false;
      }
  
      @Override
      protected final ImmutableTerm buildTermAfterEvaluation(ImmutableList<ImmutableTerm> newTerms,
                                                             TermFactory termFactory, VariableNullability variableNullability) {
          if (newTerms.stream()
                  .allMatch(t -> isRDFFunctionalTerm(t) || (t instanceof Constant))) {
              ImmutableList<ImmutableTerm> typeTerms = newTerms.stream()
                      .map(t -> extractRDFTermTypeTerm(t, termFactory))
                      .collect(ImmutableCollectors.toList());
  
              ImmutableList<ImmutableTerm> subLexicalTerms = newTerms.stream()
                      .map(t -> extractLexicalTerm(t, termFactory))
                      .collect(ImmutableCollectors.toList());
  
              ImmutableTerm lexicalTerm = computeLexicalTerm(subLexicalTerms, typeTerms, termFactory)
                      .simplify(variableNullability);
  
              // NB: Only there for improving the performance
              if (lexicalTerm.equals(termFactory.getNullConstant()))
                  return lexicalTerm;
  
              ImmutableTerm typeTerm = termFactory.getIfElseNull(
                      termFactory.getDBIsNotNull(lexicalTerm),
                      termFactory.getRDFTermTypeConstant(xsdBooleanType))
                      .simplify(variableNullability);
  
              return termFactory.getRDFFunctionalTerm(lexicalTerm, typeTerm);
          }
          else
              return termFactory.getImmutableFunctionalTerm(this, newTerms);
      }
  
      protected abstract ImmutableTerm computeLexicalTerm(ImmutableList<ImmutableTerm> subLexicalTerms,
                                                          ImmutableList<ImmutableTerm> typeTerms, TermFactory termFactory);
  }
  