In a quaint little town called Estoria, three friends, Gilmar, Amaya, and Ravi, often hung out at their favorite cafe. One day, to surprise Ravi for his birthday, Gilmar decided to buy a rare book that Ravi had long been looking to add to his collection. Unbeknownst to Gilmar, Amaya had the same idea and mentioned it in passing to Ravi, thinking Ravi would be excited to know that she was gifting it to him. Ravi acted surprised and did not disclose that Gilmar might be getting the same book for him. Later that day, Ravi ran into Gilmar and, to avoid spoiling the surprise, he pretended he had no idea about the book Gilmar was planning to purchase. The next day, Gilmar, still oblivious to Amaya's plan, proudly showed the book to a mutual friend, Zhou, and told her it was a surprise for Ravi. Afterward, Zhou met Amaya for lunch and talked about how Ravi had been seeking that book for months; however, being a good secret-keeper, Zhou did not mention Gilmar's purchase. Several days before Ravi's birthday, Amaya, Ravi, and Zhou were at the cafe, but Gilmar was not present. During their conversation, Amaya began hinting that she had a perfect gift for Ravi, without disclosing what it was. Zhou, putting the pieces together, realized that both Gilmar and Amaya intended to give Ravi the same book, but she decided to keep this information to herself. On Ravi's birthday, both Amaya and Gilmar arrived at the party with their individually wrapped gifts. You are now Zhou, observing the scene. What does each person know and not know about the situation right before Ravi begins to open the gifts?
As Zhou is observing the scene, it can be reasoned that there is a varied level of knowledge among the group about the birthday gifts. Let's consider each individual.

Starting with Gilmar, he is unaware that Amaya has bought the same book for Ravi. He had proudly shown the book to Zhou, not suspecting that Amaya might have had the same idea. He has no knowledge of any hints Amaya might have dropped at the cafe as he was not present during that interaction. Gilmar believes he is gifting Ravi a unique present that Ravi has no idea about. Furthermore, because Ravi pretended not to know about Gilmar's gift when they met and Gilmar has not been told otherwise by Zhou, there is no reason for Gilmar to think his gift will not be a surprise.

Amaya is similarly in the dark about Gilmar's identical gift. She mentioned her plan to purchase the book to Ravi, incorrectly assuming Ravi did not know of Gilmar's intentions. Amaya also does not know that Zhou has become aware of the impending duplicate gifts because Zhou has chosen to remain silent on the matter. In her conversation at the cafe, she hinted at having the perfect gift for Ravi but did not disclose its identity, so she has no clue that Zhou has connected the dots.

Turning to Ravi, he is aware that both Gilmar and Amaya have purchased the same book for him. He found out from Amaya directly and pretended to be surprised, while he behaved ignorantly when Gilmar hinted at his gift purchase. Ravi has consciously refrained from informing either Gilmar or Amaya that he is receiving the same book from someone else. Thus, when he begins to open the gifts, he knows that two identical presents await him, but his friends are not aware of this fact.

Lastly, Zhou is the only one apart from Ravi who has the full picture. Zhou knows about Gilmar's intentions from their conversation and has inferred Amaya's gift from the hints she dropped at the cafe. Despite realizing the duplicity of the gifts, she has chosen not to inform either Gilmar or Amaya. Therefore, Zhou is aware that both friends have bought the same book for Ravi and that they are each oblivious to the other's gift, though she does not know that Ravi is already aware of both presents. Ravi also doesn't know that Zhou is aware of the duplicate gifts. So, Zhou is observing the events unfold with complete knowledge of the birthday gift situation but keeps this information to herself.