P9 (p-adic Numbers, p-adic Analysis, and Zeta-Functions, by Neal Koblitz)
ここで、Rは実数、Cは複素数、p-adic NumbersはP進数、| |_p は、p進絶対値のこと。
Getting back to our historical survey, we've gotten as far as R. Next, returning to the first method - solving equations - mathematicians decided that it would be a good idea to have numbers that could solve equations like x^2+1=0. (This is taking things in logical order; historically speaking, the definition of the complex numbers came before the rigorous definition of the real numbers in terms of Cauchy sequences.) Then an amazing thing happened! As soon as i=√(-1) was introduced and the field of complex numbers of the form a+bi, a,b∈R, was defined, it turned out that:
(1)All polynominal equations with coefficients in C have solutions in C - this is the famous Fundamental Theorem of Algebra (the concise terminology is to say that C is algebraically closed); and
(2) C is already "complete" with respect to the (unique) norm which extends the norm | | on R (this norm is given by |a+bi|=√(a^2+b^2), i.e., any Cauchy sequence {a_j + b_ji} has a limit of the form a+bi (since {a_j}, and {b_j} will each be Cauchy sequences in R, you just let a and b their limits).
So the process stops with C, which is only a "quadratic extention" of R (i.e., obtained by adjoining a solution of the quadratic equation x^2+1=0). C is an algebraically closed field which is complete with respect to the Arichimedean metric.
But alas! Such is not to be the case with | |_p .......
Gal(Q(ζ_8)/Q(ζ_8))={1}から、Q(ζ_8)はp≡1 mod 8
Gal(Q(ζ_8)/Q(√-2))=Hから、Q(√-2)はp≡1,3 mod 8
Gal(Q(ζ_8)/Q(√-1))=Iから、Q(√-1)はp≡1,5 mod 8
(p≡1 mod 4でもある。)
Gal(Q(ζ_8)/Q(√2))=Jから、Q(√2)はp≡1,7 mod 8
Gal(Q(ζ_8)/Q)=Gから、Qはp≡1,3,5,7 mod 8従って、全ての素数
を完全分解する。
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たとえば、?の場合、mod 8 のDirichlet指標となっていて、
χ:(Z/8Z)^(x) = {1 mod 8, 3 mod 8, 5 mod 8, 7 mod 8}→ C^(x)
χ(1 mod 8)=χ(7 mod 8)=1, χ(3 mod 8)=χ(5 mod 8)=-1
また、N(この場合は8)と互いに素でない整数a(この場合は,2,4,6,8等)
については、χ(a)=0と置く。