Byron beats up kids who are walking to school, and takes the…

Byron beats up kids who are walking to school, and takes their lunch money.  He only does this with kids who are smaller than he is, not if the kid is bigger.   In the past, he has always been able to get the money from small kids, but not from big kids, who have sometimes beat Byron up. Byron’s physical assaults and stealing behavior, being reliably evoked in the presence of a small kid walking alone to school, exemplifies which of the following principles of behavior?