"You-you-you, this is..." Xie Kefu stammered.
"Doing problems is too tiring. I'm getting some oxygen." Song He explained.
Xie Kefu scratched his yellow hair. "When I'm tired, I drink. You inhale oxygen. Your habit looks healthier."
He walked behind Song He and bent over to look at the paper on the screen.
Several familiar-looking formulas entered his eyes. After a brief hesitation, he recalled something, and his expression changed.
"This paper is related to the Calabi Conjecture! Can you understand it?" Xie Kefu asked.
"No. I'll learn it slowly." Song He looked miserable. "Have you studied it?"
"When I was a sophomore, I tried to teach myself. It was so difficult it made me want to vomit. I only understood the basics." Xie Kefu advised him, "You don't need to waste time on knowledge that's too difficult. Learn the simple stuff first, then study this in a couple of years. How about eating breakfast?"
"I'm not hungry." Song He raised his pen and wrote a long string of formulas on the paper, frowning as he worked through the deduction.
Xie Kefu watched the formulas curiously. The difficulty was horrifying.
It was obvious that Song He had gotten stuck too. He hesitated, writing a couple of strokes after a long while, then quickly crossed them out. He looked just like a bottom-ranked student caught between advancing and retreating in an exam, without the slightest trace of a top student's effortless confidence.
"Why are you studying this extra material?" Xie Kefu asked curiously. "You can't understand it anyway."
"I'm looking for a way to cause a qualitative transformation in the Space Window-Cleaning Bug program." Song He said confidently, "I'll understand it!"
Xie Kefu looked skeptical. "You have an idea?"
"Not yet. I haven't learned enough."
Xie Kefu left the dormitory, then returned