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.ImmutableExpression;
  import it.unibz.inf.ontop.model.term.ImmutableFunctionalTerm;
  import it.unibz.inf.ontop.model.term.ImmutableTerm;
  import it.unibz.inf.ontop.model.term.TermFactory;
  import it.unibz.inf.ontop.model.type.RDFDatatype;
  import it.unibz.inf.ontop.model.type.RDFTermType;
  import it.unibz.inf.ontop.model.type.TermTypeInference;
  import it.unibz.inf.ontop.model.vocabulary.SPARQL;
  
  import javax.annotation.Nonnull;
  import java.util.Optional;
  
  /**
   * SPARQL's strict equality function symbol
   */
  public class SameTermSPARQLFunctionSymbolImpl extends SPARQLFunctionSymbolImpl {
  
      private final RDFDatatype xsdBooleanType;
  
      protected SameTermSPARQLFunctionSymbolImpl(@Nonnull RDFTermType rdfRootType, RDFDatatype xsdBooleanType) {
  
          super("SP_SAME_TERM", SPARQL.SAME_TERM, ImmutableList.of(rdfRootType, rdfRootType));
          this.xsdBooleanType = xsdBooleanType;
      }
  
      /**
       * Always simplifies itself
       */
      @Override
      protected ImmutableTerm buildTermAfterEvaluation(ImmutableList<ImmutableTerm> newTerms, TermFactory termFactory,
                                                       VariableNullability variableNullability) {
          ImmutableExpression condition = termFactory.getStrictEquality(newTerms);
  
          ImmutableFunctionalTerm lexicalTerm = termFactory.getConversion2RDFLexical(condition, xsdBooleanType);
          ImmutableFunctionalTerm typeTerm = termFactory.getIfElseNull(
                  termFactory.getDBIsNotNull(condition),
                  termFactory.getRDFTermTypeConstant(xsdBooleanType));
  
          return termFactory.getRDFFunctionalTerm(lexicalTerm, typeTerm)
                  .simplify(variableNullability);
      }
  
      @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;
      }
  }
  