public Person addPerson(string lastname, string firstname, PersonType type)
 {
     Person unePersonne = new Person
         {
             Date = DateTime.Now,
             LastName = lastname,
             FirstName = firstname,
             PersonType = type,
             HasSubscribed = false
         };
     _persons.Add(unePersonne);
     return unePersonne;
 }
 /*Must change the boolean property of the Person in your list to true*/
 public bool Subscribe(Person p)
 {
     try
     {
         Person newPerson = _persons.Find(pe => pe.FirstName.ToLowerInvariant() == p.FirstName && pe.LastName.ToLowerInvariant() == p.LastName);
         if (newPerson==null)
         {
             return false;
         }
         newPerson.HasSubscribed = true;
         return true;
     }
     catch (Exception)
     {
         return false;
     }
 }