Elements of Number Theory (Undergraduate Texts in by John Stillwell

By John Stillwell

Strategies of equations in integers is the significant challenge of quantity idea and is the focal point of this publication. the volume of fabric is appropriate for a one-semester path. the writer has attempted to prevent the advert hoc proofs in desire of unifying rules that paintings in lots of events. There are routines on the finish of just about each part, in order that each one new inspiration or facts gets rapid reinforcement.

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We denote by Un1 the subgroup {x ∈ Un : x ≡ 1 mod pn }. More generally, if Z is any subgroup of Un , we write Z 1 = Z ∩ Un1 . 4 Iwasawa’s Theorem 53 Note that the index of Z 1 in Z always divides p − 1, because Z 1 is the kernel of the reduction map from Z into F× p . In particular, this index 1 1 is prime to p. Also, note that Un and Un are now Zp -modules, whereas this is plainly not true for Un and Un themselves. 9) taken with respect to the norm maps. Since Un1 and Cn1 are compact 1 and C 1 .

12). 2. For all k ≥ 1, and all u in U∞ , we have G ˜ χ(g)k dL(u) = (1 − pk−1 )δk (u). 12) Proof. 10) gives G χ(g)k dλ = Z× p xk d(χ(λ)). ˜ Also, via our identification of Λ(Z× p ) with a subset of Λ(Zp ), the integral above on the right has the same value if we integrate over the whole ˜ ˜ of Zp . Now take λ = L(u), so that, by definition, we have χ( ˜ L(u)) = Υ(L(fu )), where we recall that L(fu )(T ) = fu (T )p 1 . 12) is equal to Dk−1 (hu (T ) − ϕ(hu )(T )) T =0 , where hu (T ) = (1 + T ) fu (T ) .

Let f be in W . Recalling that ϕ(f )(T ) = f ((1 + T )p − 1) and applying ∆ to the equation f (ξ(1 + T ) − 1), ϕ(f ) = ξ∈µp we obtain immediately that ψ(∆(f )) = ∆(f ). The final assertion of the lemma is obvious. In fact, the following stronger result is true, but its proof is subtle and non-trivial. 6. We have ∆(W ) = Rψ=1 . The strategy of the proof is to use reduction modulo p. 9) and let x → x be the reduction map. If Y is any subset of R, then we denote by Y its image in Ω under the reduction map.

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