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john mangual
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Hasse-Weil Bound and Chebyshev Inequality

I was reading about the Hasse-Weil bound for the number of points in on a curve over the finite field $\mathbb{F}_q$.

$$ \big| |C(\mathbb{F}_q)| - (q+1) \big| \leq 2g \sqrt{q} $$

However, this reminded me quite a bit of the Chebyshev inequality.

$$ \mathbb{P}\big[ |X - \mathbb{E}[X]| \geq k \sigma \big] \leq \frac{1}{k^2} $$

Is there a way to prove - or at least interpret - the Hasse-Weil bound as an estimate of the "Expected" number of points on a curve?


Maybe if we do the correspondence $X \mapsto |C(\mathbb{F}_q))| $ , so the random variable is the number of points of the curve.

Then $k \mapsto g$ so the genus can be read as the number of "standard deviations" away from the norm.

We can even justify $\mathbb{E}[X] \mapsto q+1$ since a generic projective curve $f(x,y,z) = 0$ should have one solution for every $x \in \mathbb{F}_qP^1$ which has $q+1$ elements.

john mangual
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