Examination room dialogue

On one test, the invigilator found a note under the student desk.

The teacher asked: "Is this yours?"

The student replied: "No!"

“No?” the teacher said. “Don’t argue, is it yours?”

"Really not!" The students still don't recognize it.

The teacher said: "You honestly say, I will not punish you!"

The student pointed to a piece of paper under the pencil case and said, "This is mine!"