有理点 [rational-points]

$\gdef\ul#1{\underline{#1}}$ $\gdef\spaces#1{~ #1 ~}$ $\gdef\quads#1{\quad #1 \quad}$ $\gdef\eqq{\quads=}$ $\gdef\R{\mathbf{R}}$ $\gdef\Q{\mathbf{Q}}$