public Pupil AddPupil(string firstName, string lastName)
{
if (firstName == null ||
lastName == null ||
firstName.Length < 2 ||
lastName.Length < 2)
{
throw new ArgumentException();
}
if (_pupils.FirstOrDefault(p => p.FirstName == firstName && p.LastName == lastName) != null)
{
throw new ArgumentException();
}
var newOne = new Pupil(this, firstName, lastName);
_pupils.Add(newOne);
return(newOne);
}
