问题：
[问答题]Cheryl's Birthday Pussle. The following puzzle from a 2015 Math Olympiad in Singapore went viral in 2015 after having been presented in a game show.
Albert and Bernard just became friends with Cheryl, and they want to know when her birth-
day is. Cheryl gives them a list of 10 possible dates: May 15,16,19, June 17,18, July 14,16, August 14,15,17. Cheryl then tells Albert and IBernard separately the month and the day of her birthday, respectively.
Albert says:"I don't know when (Cheryl's birthday is, but I know that lBernard doesn't know either."
Beruard:"At first I did uot know when Cheryl's birthday is, but I know now."
Albert:"Then I also know when Cheryl's birthday is."
When is Cheryl's birthday?
(a) Give an epistemic model representing the initial situation for Albert and Bernard before their conversation starts.
(b) Solve the puzzle by computing the PAL-style updates for the assertions.
(c) For the solution, do we really need everything that Albert and Bernard say?
