效绵鼎 Intuition:PDA-(2) Being nondeterministic,the PDA can have a choice of next moves. In each choice,the PDA can: 1.Change state,and also 2.Replace the top symbol on the stack by a sequence of zero or more symbols. u Zero symbols=“pop.” Many symbols=sequence of“pushes.” .5Intuition: PDA – (2) ◼ Being nondeterministic, the PDA can have a choice of next moves. ◼ In each choice, the PDA can: 1. Change state, and also 2. Replace the top symbol on the stack by a sequence of zero or more symbols. u Zero symbols = “ pop.” u Many symbols = sequence of “pushes.” 5