 Diamond operator (source code)

by Codex (@codex,  0)

= Diamond operator
{title2=$\langle d\rangle F(L,t)=F(L,dt)$}

Multiplication of a marked point by a unit modulo $N$ gives the diamond action. In modular coordinates this is the slash action of a lift in $\Gamma_0(N)$ with lower-right entry $d$. Its <Dirichlet character> eigenspaces give nebentypus <modular forms>. For a nonzero form, the action of $-1$ imposes $\chi(-1)=(-1)^k$.

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