J. Rouse and D. Zureick-Brown have classified all possible images $G$ of the 2-adic Galois representation attached to an elliptic curve defined over $\Q$, in terms of the index $n$ of $G$ in $\GL(2,\Z_2)$, the level $l=2^k$, and explicit generators of $G$.

The **Rouse level** $l=2^k$ is the smallest power of $2$ such that $G$ contains the kernel of reduction modulo $l$. The exponent $k$ is called the **Rouse log-level**. The **Rouse index** of $G$ is the index $[\GL(2,\Z_2):G]$.

The **Rouse generators** of $G$ are a finite set of matrices in $\GL(2,\Z/l\Z)$ whose pull-backs to $\GL(2,\Z_2)$ generate $G$.

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- Last edited by John Jones on 2018-06-19 16:09:51

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- 2018-06-19 16:09:51 by John Jones (Reviewed)