Modular Curves $X_1(n)$ as Moduli of Point Arrangements
Lev Borisov
For a complex elliptic curve $E$ and a point $p$ of order $n$ on
it, the images of the points $p_k=kp$ under the Weierstrass
embedding of $E$ into $CP^2$ are collinear if and only if the sum
of indices is divisible by $n$. We prove that for $n$ at...