Sato's interpreter cannot be Yuna as it is stated that if Sato's interpreter is not Yuna, the only other known interpreter is Hiroto. Since Akira and Sato have conversed with Hiroto's help, it indicates Hiroto is also Sato's interpreter implying he serves dual roles. Yuna, being Keiko's interpreter, has the role of facilitating communication for Keiko with other non-Japanese speaking participants. Keiko might interact with Hiroto only when she is engaged in conversations involving Akira or Sato or when requiring his services in the absence of Yuna. However, the information provided does not necessarily indicate any direct interaction between Keiko and Hiroto except through the diplomatic or interpretive necessities of the conference.
At an international conference, there are three diplomats: Akira, Keiko, and Sato. Each diplomat is accompanied by an interpreter. Akira's interpreter is named Hiroto. Keiko's interpreter is someone named Yuna. If Sato's interpreter is not Yuna, and Akira and Sato have been seen conversing with Hiroto's help, who is Sato's interpreter and what role does Yuna have at the conference? Also, describe what interaction Keiko might have with Hiroto. Provide a very brief response.