code: package org.optsol.project_scheduling.mrcpsp.fct.constraints;
  
  import com.google.ortools.linearsolver.MPConstraint;
  import com.google.ortools.linearsolver.MPSolver;
  import com.google.ortools.linearsolver.MPVariable;
  import java.util.Collection;
  import java.util.HashSet;
  import org.optsol.jdecor.core.AbstractVariableManager;
  import org.optsol.jdecor.ortools.AbstractOrtoolsConstraintManager;
  import org.optsol.project_scheduling.mrcpsp.constants.sub.IConstants_V;
  import org.optsol.project_scheduling.mrcpsp.fct.variables.DecisionVars_Fct;
  
  public class FCT_d_UniqueOrderIfSequentially<CONST extends IConstants_V>
      extends AbstractOrtoolsConstraintManager<CONST> {
  
    public FCT_d_UniqueOrderIfSequentially() {
      super("i", "j");
    }
  
    @Override
    protected Collection<ConstraintKey> createKeys(CONST constants) {
      HashSet<ConstraintKey> indexes = new HashSet<>();
      for (int i : constants.get_V()) {
        for (int j : constants.get_V()) {
          if (i < j) {
            indexes.add(new ConstraintKey(i, j));
          }
        }
      }
      return indexes;
    }
  
    @Override
    protected void configureConstraint(
        MPConstraint constraint,
        CONST constants,
        AbstractVariableManager<MPSolver, MPVariable> variables,
        ConstraintKey index) throws Exception {
      int i = index.get("i");
      int j = index.get("j");
  
      constraint.setUb(1.);
  
      constraint.setCoefficient(variables.getVar(DecisionVars_Fct.y, i, j), 1.);
      constraint.setCoefficient(variables.getVar(DecisionVars_Fct.y, j, i), 1.);
    }
  }
  