private void removeTransaction(IPerson person, IBook book)
{
if (!this.transactions.ContainsKey(person))
{
throw new BorrowException("This person (" + person.ID + ") doesn't borrow any book.");
}
else
{
if (this.transactions[person].Contains(book))
{
book.incrementCounter();
this.transactions[person].Remove(book);
}
else
{
throw new BorrowException("This person (" + person.ID + ") doesn't borrow this book (" + book.ISBN + ").");
}
}
}