"Got it."
Yuki felt uneasy at Riku's short reply.
"Do you really understand?"
"I said I got it, didn't I?"
The club room atmosphere grew a bit heavy.
"This is a typical conversation lacking redundancy," Aoi observed.
"Lacking redundancy?" Yuki asked.
"Insufficient necessary information. A 1-bit response of 'got it' doesn't clarify what or how he understood."
Riku objected. "But I listened to the explanation, so I 'got it.'"
"But," Aoi said quietly, "Yuki doesn't know your level of understanding."
"Then what should I say?"
"For example, 'Got it. So we're meeting at the station at 9 tomorrow, right?' for confirmation."
"Isn't that redundant?" Riku complained.
"That's the value of redundancy. Error detection and confirmation become possible."
Yuki understood. "By repeating, we can confirm there's no misunderstanding."
"Yes. In communication theory, it's called ACK (acknowledgment)."
Aoi drew a diagram on the whiteboard. Sender, message, receiver, ACK.
"When the receiver confirms understanding and returns it, the sender knows it was conveyed correctly."
Riku thought. "But isn't repeating everything tedious?"
"It's a tradeoff between efficiency and robustness," Aoi explained. "Reducing redundancy is efficient but vulnerable to errors."
"Like just sending 'OK' in chat?" Yuki gave an example.
"Exactly. Short, but what you're OK-ing is unclear."
Riku was convinced. "So more important things need more redundancy?"
"Yes. Emergency communications always repeat for confirmation. Like air traffic control."
Aoi gave another example. "'Tower, cleared to runway 34R' 'Copy, cleared to runway 34R.'"
"They're repeating," Yuki noticed.
"Because the cost of error is high. Lives are at stake."
Riku became serious. "So even in conversations with friends, redundancy is necessary?"
"Depends on context. With close friends, there's much shared knowledge, so you can abbreviate."
"Shared knowledge is like a dictionary?"
"Yes. But new topics or important promises should increase redundancy."
Yuki gave a real example. "Just 'Tomorrow' leaves time and place unknown."
"Right. 'Let's meet at the library at 3 PM tomorrow' is specific."
Riku laughed. "Do I always abbreviate too much?"
"A bit," Aoi smiled. "But that's also very you."
"What do you mean?"
"Perfect redundancy is mechanical and cold. Moderate abbreviation is also proof of intimacy."
Yuki understood. "Because there's trust, we can abbreviate."
"Exactly. The optimal level of redundancy depends on the relationship."
Riku looked out the window. "So what's the redundancy of our conversations?"
"On the low side, but functional," Aoi evaluated. "Because there's effort to understand each other."
"Effort?"
"Effort to read context, effort to ask questions, effort to confirm."
Yuki added. "Even with low redundancy, if decoding ability is high, it gets through."
"Wonderful summary," Aoi was impressed.
Riku stood up. "Got it. So we adjust redundancy according to the situation."
Aoi and Yuki laughed.
"That response had appropriate redundancy," Aoi acknowledged.
"I learned," Riku puffed his chest.
"But," Yuki said, "sometimes increase redundancy. Because I worry."
"Got it. Sorry for worrying you. From now on, I'll explain more specifically."
Aoi nodded with satisfaction. "Perfect. This is adaptive redundancy."
The three laughed together. It was a day when they learned something important from a conversation lacking redundancy.