I'm having trouble understanding this block of definitions: Definition: Let A = {} a_1 elementof A_1 Lambda...Lambda a_p elementof A_p} be a set of joint strategies over p players. Definition: For any p elementof P, a_p' elementof A_p, and a elementof A, let a||a_p' denote the member of A obtained by replacing a_p with a_p'. This is called a unilateral defection from the joint strategy a by player p. It's really the first two definitions that I'm confused about. What is A supposed to represent, and what is the difference between A and A_n? I'm also not sure what unilateral defection is, or why it is called that. I think understanding the first definition will help clarify the other ones