prologue i   nayeon thinks back to before; past trigonometry, past geometry, tries to flip imaginary pages in the back of her head as she thinks past all those recent lessons and tries to go to the very beginning of things. think, nayeon, think. her pen tapping against her test paper, her feet becoming restless, the space between her eyebrows forming creases as she digs her brain for the right answer.   which one was it? did it start with a b? a d? what thereom was it that frustrated nayeon so much one rainy night; bending over her study desk and neglecting her posture as she scribble down solutions and numbers and equations to shove in her annoying math teacher's face?    "ten more minutes," comes the distant-sounding voice of their homeroom adviser. distant, yet nayeon still hears it and she's already beginning to crack.   she mumbles a curse word under her breathe that would make her parents look twice at her with angry-surprise while her brother would smile and nod, stating how he finally saw that they really were siblings.    and then it suddenly comes to her, a tidal wave - no, no, no, a tsunami of a word that washes her confusions and doubts clean off of her.    pythagorean, damn it!    everything just becomes crystal clear to her from then on, as it sometimes should be. when im nayeon remembers, oh boy, does she remember.   she finishes the question smoothly, finally and she continues  to scrawl answers through the last remaining questions, recalling how the pythagorean thereom was named after the greek mathematician who created it, his name was pythagoras and he stated that in any right triangle, the area of the square whose side is the hypotenuse, is equal to the sum of the areas of the squares whose sides are the two legs.   easy to memorize but a bit of a challenge to actually apply it, even for im nayeon.   out of all the sections in math, she hate, hate, hate, hated calculus the most. not only was it a bore, but when she finally acted like she was even listening, it all made no sense and even if she did really listen and tried to comprehend, strings would tug at the back of her mind, telling her she won't need calculus once she gets into college. (at least that's what jaebum's been blabbering about but easy for him to say, he's in law!)   when the bell rings, nayeon is falling into step beside jisoo as they both walk out their classroom. she has her chin up, and a smile gracing her lips meanwhile the guy beside her is not quite as half as cheerful as she is, barely one-fourth if you asked her.    "math will be the death of my grades," jisoo mumbles, knuckles turning white before he sighs, trying to release all the negativity into that one action. "goodbye seoul university, goodbye yonsei."   she laughs, nudges him by the side and tells him it's not the end of the world at all. "well, there's still that science quiz i'm a hundred percent sure you aced, and home economics. i think you'll do fine." she says, just to lighten his current mood but jisoo is in a no-jam phase thus making her drag him towards the frozen yogurt stand right outside of the school gates before dropping by the local dvd store a few blocks from where she lived.    "ohh, new stock." the smile on her face (because