The invariants of the Weil representation of $\mathrm{SL}_2(\mathbb{Z})$
The transformation behaviour of the vector valued theta function of a positive-definite even lattice under the metaplectic group $\mathrm{Mp}_2(\mathbb{Z})$ is described by the Weil representation. We show that the invariants of this representation are induced from $5$ fundamental invariants.
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Number Theory
