Poll 16

Correct answers will be shown after due date.

Multi-answer questions : 2 out of 4 unless otherwise noted.

Recall: pick the simplest language classification when in doubt -- "can't go lower than this"

 * example :  (0+1)* is regular and context-free , but we call it regular -- as it has that simple a structure

 * example : { 0^n 1^n : n >= 0 }  is context-free  (because we can't go any lower) - has at least this kind of structure

 * example : { <D> : D is a DFA with an empty language } : we call it recursive, even though it qualifies to be recursively enumerable