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* Editorial comments: *Langlands spent 1967-68 visiting in Ankara, Turkey, and while there wrote this letter to Serre. In it occurs for the first time the question of how to account for `special' representations of the Galois group, such as at primes where an elliptic curve has unstable bad reduction, corresponding to special representations of \(\mathrm{GL}_2\). This correspondence was later expanded to the Deligne-Langlands conjecture, proven eventually by Kazhdan and Lusztig.

* Author's comments: This letter is a response to a question of Serre about the gamma-factors appearing in the functional equations of automorphic \(\ell\)-functions. Fortunately Serre's letter to me was accompanied by several reprints, among them apparently the paper* Groupes de Lie \(\ell\)-adiqes attachées aux courbes elliptiques

*that appeared in the volume*

**Les tendances géométriques en algèbre et théorie des nombres**.*Although the letter promised in the last line was never written, it is clear what I had in mind. Sometime soon after writing the letter to Weil, perhaps even at the time of writing, I was puzzled by the role of the special representations. The solution of the puzzle was immediately apparent on reading Serre's paper which treated the \(\ell\)-adic representations associated to elliptic curves whose \(j\)-invariant was not integral in the pertinent local field. The special representations of \(\mathrm{GL}(2)\) corresponded to these \(\ell\)-adic representations. The connection between non-semisimple \(\ell\)-adic representations and various kinds of special representations is now generally accepted. The theorem of Kazhdan-Lusztig is a striking example.*