Preface

There is a “disagreement” between lecture slides and textbook regarding the use of popping $\epsilon$ (e.g. nothing) from the stack for a move.

• Lecture slides say yes, this is possible. (e.g. $\delta(q_0, a, \epsilon, a)$ when in state $q_0$, reading input symbol $a$, can pop nothing from the stack and push $a$ to the top of the stack.
• Textbook says no, a symbol must always be popped from the stack on each move.

Will be following the lecture slides when designed PDA/NPDA’s.