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devoted to a proof of this. The proof is standard; for another reference, see Theorem~2.15
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of~\cite{ddt}.
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\section{The $\ell$-torsion in the Frey curve is hardly ramified.}
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\section{The l-torsion in the Frey curve is hardly ramified.}
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Let $(a,b,c,\ell)$ be a Frey package, with associated Frey curve $E$ and mod $\ell$ Galois
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representation $\rho=E[\ell]$. We now work through a proof that $\rho$ is hardly ramified.
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\begin{theorem}\label{Frey_curve_good} If $p\not=\ell$ is a prime not dividing $abc$ then
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$\rho$ is unramified at~$p$.
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\end{theorem}
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\begin{proof} Indeed, $E$ has good reduction at $p$, and hence $\rho$ is unramified at $p$ by~ref{good_reduction_implies_unramified}.
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\begin{proof} Indeed, $E$ has good reduction at $p$, and hence $\rho$ is unramified at $p$
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by~\ref{good_reduction_implies_unramified}.
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\end{proof}
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If however $p$ divides $abc$ then $E$ has multiplicative
@@ -265,8 +266,12 @@ \section{The $\ell$-torsion in the Frey curve is hardly ramified.}
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\begin{theorem}\label{Frey_curve_mod_ell_rep_at_ell} Let $\rho$ be the $\ell$-torsion in the
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Frey curve associated to a Frey package $(a,b,c,\ell)$. Then the restriction of $\rho$ to $\GQl$ comes from a finite flat group scheme.
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\end{theorem}
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\begin{proof} The Frey curve either has good reduction at $\ell$ (case 1 of FLT) or multiplicative reduction at $\ell$ (case 2 of FLT). In the first case the $\ell$-torsion is finite and flat
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at $\ell$ by theorem~ref{good_reduction_implies_flat}. In the second case the theory of the Tate curve shows that the $\ell$-torsion is (up to quadratic twist) an \emph{unramified} extension of the trivial character by the cyclotomic character, and furthermore that the extension is controlled
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\begin{proof} The Frey curve either has good reduction at $\ell$ (case 1 of FLT) or multiplicative
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reduction at $\ell$ (case 2 of FLT). In the first case the $\ell$-torsion is finite and flat
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at $\ell$ by theorem~\ref{good_reduction_implies_flat}. In the second case the theory of the Tate
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curve shows that the $\ell$-torsion is (up to quadratic twist) an \emph{unramified} extension of
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the trivial character by the cyclotomic character, and furthermore that the extension is
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controlled
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by the $\ell$th power of an $\ell$-adic unit. This extension is known to be finite and flat;
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see for example Proposition~8.2 of~\cite{edix}.
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\end{proof}
@@ -284,7 +289,7 @@ \section{The $\ell$-torsion in the Frey curve is hardly ramified.}
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theorem~\ref{frey_curve_at_2}, and the fourth is theorem~\ref{Frey_curve_mod_ell_rep_at_ell}.
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\end{proof}
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\section{The $\ell$-torsion in the Frey curve is irreducible.}
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\section{The l-torsion in the Frey curve is irreducible.}
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We finish this chapter by showing that Mazur's theorem implies that the $\ell$-torsion in the Frey
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