Algebraic Patching by Moshe Jarden

By Moshe Jarden

Assuming merely simple algebra and Galois idea, the publication develops the strategy of "algebraic patching" to achieve finite teams and, extra commonly, to resolve finite cut up embedding difficulties over fields. the tactic succeeds over rational functionality fields of 1 variable over "ample fields". between others, it results in the answer of 2 critical leads to "Field Arithmetic": (a) absolutely the Galois staff of a countable Hilbertian pac box is unfastened on countably many turbines; (b) absolutely the Galois team of a functionality box of 1 variable over an algebraically closed box $C$ is freed from rank equivalent to the cardinality of $C$.

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I=1 ˜ Suppose u10 , . . , um0 are linearly independent over K, f ∈ K[[x]] 0 , and f (0) = 0. Then f1 , . . , fm ∈ K[[x]]0 . Proof: We break up the proof into several parts. Part A: Comparison of norms. We consider the K-vector space V = m i=1 Kui0 and define a function μ: V → R by m (4) ai ui0 ) = max(|a1 |, . . , |am |). μ( i=1 It satisfies the following rules: (5a) μ(v) > 0 for each nonzero v ∈ V . (5b) μ(v + v ) ≤ max(μ(v), μ(v )) for all v, v ∈ V . (5c) μ(av) = |a|μ(v) for all a ∈ K and v ∈ V .

1: The fields K((x)) and K((x1/p ))0 are linearly disjoint over K((x))0 . Proof: First note that 1, x1/p , . . , xp−1/p is a basis for K(x1/p ) over K(x). Then 1, x1/p , . . , xp−1/p have distinct v-values modulo Z = v(K((x))), so they are linearly independent over K((x)). Next we observe that 1, x1/p , . . , xp−1/p also generate K((x1/p )) over K((x)). Indeed, each f ∈ K((x1/p )) may be multiplied by an appropriate Chapter 2. Normed Rings 26 power of x to be presented as ∞ (1) an xn/p , f= n=0 with a0 , a1 , a2 , .

Notes 29 Now we choose a basis u10 , . . , um0 for F¯ /K and lift each ui0 to an ˜ element ui of F ∩ K[[x]] 0 . Then, u1 , . . , um are linearly independent over K((x))0 and over K((x)), hence they form a basis for F/K((x))0 and for Fˆ /K((x)). As before, F = K((x))F is the completion of F . Again, both F and F have the same residue field F and [F : Fˆ ] = [F : F¯ ]. Note that F ⊆ K 1/p and [F : F¯ ] ≤ [F : F ] = p. Therefore, F = F¯ or [F : F¯ ] = p. In the first case f ∈ Fˆ , so by the paragraph before the preceding one, m there exist f1 , .

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