Having set up the general theory of valued fields, we now return to algebraic number fields. We want to develop their basic theory from the valuation-theoretic point of view. This approach has two prominent advantages compared to the ideal-theoretic treatment given in the first chapter. The first one results from the possibility of passing to completions, thereby enacting the important “local-to-global principle”. This will be done in chapter VI. The other advantage lies in the fact that the archimedean valuations bring into the picture the points at infinity, which were hitherto lacking, as the “primes at infinity”. In this way a perfect analogy with the function fields is achieved. This is the task to which we now turn.
KeywordsExact Sequence Prime Ideal Short Exact Sequence Number Field Grothendieck Group
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