Let $C$ be the image of a canonical embedding $\phi$ of the Atkin--Lehner quotient $X_0^+(N)$ associated with the Fricke involution $w_N$.
In this note we exhibit some relations among the rational points of $C$. For each $g=3$ (respectively the first $g=4$) curve $C$ we found that there are one or more
lines (respectively planes) in $\PP^{g-1}$ whose intersection with $C$ consists entirely of rational Heegner points or the cusp point, where $N$ is prime.
We also discuss an explanation of the first nonhyperelliptic exceptional rational point.
@article{1259158425,
author = {Casta\~no-Bernard, Carlos},
title = {A Note on the Rational Points of $X\_0^+(N)$},
journal = {Experiment. Math.},
volume = {18},
number = {1},
year = {2009},
pages = { 129-135},
language = {en},
url = {http://dml.mathdoc.fr/item/1259158425}
}
Castaño-Bernard, Carlos. A Note on the Rational Points of $X_0^+(N)$. Experiment. Math., Tome 18 (2009) no. 1, pp. 129-135. http://gdmltest.u-ga.fr/item/1259158425/