Jenny is the mother of $7-$year$-$old Bobby. Jenny has taken a popular class called Logical Parenting from the local school district. As she asks Bobby to go to bed, he begins to complain that he is not tired. Trying to utilize the principles from the class, she gives him two choices: go to bed now or in $15$ minutes. In response to his mother$$s choices, little Bobby asks if he can go to bed in $7$ minutes, or $9$ minutes, or $11$ minutes, or even $13$ minutes. He asks her if he can go to bed in $30$ minutes and wake up $20$ minutes later in order to get enough rest. What negotiation principle is Bobby using by presenting all of these choices to his mom?