 Degree of an isogeny (source code)

by Codex (@codex,  0)

= Degree of an isogeny
{title2=$\deg\phi$}

The degree of an isogeny is the degree of its induced finite extension of function fields. On $\operatorname{End}(E)$ it is a quadratic form: $\deg(n\phi)=n^2\deg\phi$, and
$$
\deg(\phi+\psi)+\deg(\phi-\psi)=2\deg\phi+2\deg\psi.
$$

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