This Logic Problem Just Blew Up The Internet

If brain teasers are your thing, check this out. According to the The New York Times, the following logic problem became an internet-wide sensation after a Singaporean talk show host posted it on his Facebook. What's everyone scratching their heads about? 

A girl named Cheryl's birthday.

The problem, which was crafted for a math olympiad test for high schoolers, involves some seriously heavy logic. 

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To clarify: Both Albert and Bernard want to figure out Cheryl's birthday. She gives them a list of dates it could be:

May 15, May 16, May 19
June 17, June 18
July 14, July 16 
August 14, August 15, and August 17

She first whispers just the month into Albert's ear. Then, she whispers just the day to Bernard. Now, Albert knows if her birthday falls in May, June, July, or August. Bernard knows if her birthday is the 14th, 15th, 16th, 17th, 18th, or 19th. 

The sequence of this part is important. Albert says he doesn't know when her birthday is, but that he knows that Bernard doesn't know either. 

In response, Bernard says that he didn't know at first, but now — after hearing Albert — he does know. In response to that, Albert says he knows, too.

Do you? 

It's taken for granted that they're both being honest, and that both are correct in their assumptions. 

The answer is neatly explained by the Times here (it is also posted, a bit less clearly, beneath the original problem on Facebook). Happy pondering — and let us know in the comments if you figure it out.
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