public class MinVisitor: Visitor{
  public int Visit (IntInterval iv){
    return Math.Min(iv.From, iv.To);
  }

  public int Visit (IntSingular iv){
    return iv.TheInt;
  }

  public int Visit (IntCompSeq iv){
    return Math.Min(iv.First.Accept(this), 
                    iv.Second.Accept(this));
  }
}