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简单根式扩张上的并行积分 II:混合塔

Parallel Integration over Simple Radical Extensions II: Mixed Towers

Sam Blake

arXiv 2609.13643首次发表:更新:

AI 中文总结

本文在混合塔中移除封闭性假设,将并行Risch方法推广至任意位置的简单根式扩张,给出统一的赋值引理与次数界,并返回非初等性的证书。

AI 中文摘要

在第一部分中,我们将支撑Risch--Norman(并行Risch)方法的结构定理推广到微分域$K=F(t_1,\dots,t_n)$(在推导下封闭)的简单根式扩张$L=K(y)$,$y^m=q$。在此,我们移除封闭性假设:根式可以位于塔中的任意位置,因此其上方生成元的导数涉及$y$——即Bronstein混合初等函数算法的设定。工作环为$\cA=\cO[t_{j+1},\dots,t_n]$,即$F[t_1,\dots,t_n]$在$L$中的整闭包:它是一个Krull域,在Trager基上作为多项式环的自由模,因此所有因式分解仍发生在唯一分解整环中。推导的分母不再是元素,而是$\cA$上的一个因子$\fd_D$,赋值引理在正规高度一素理想处取统一形式$v_P(Dg)=v_P(g)-(1+v_P(\fd_D))$,涵盖了第一部分中的位移$\{1,e_P\}$;其证明是局部化的,无需消去分析。类群和单位群的稳定性,$\Cl(\cA)\cong\Cl(\cO)$及$\cA^*=\cO^*$,将可容许的对数项分为$\cO$的$S$-单位(由第一部分的机制计算)和在上层变量中移动的不可约多项式,其留数必须是常数。我们证明了顶层变量的次数界,并描述了所得算法——与经典并行方法(其失败不证明任何事)不同,该算法在两种情况下返回非初等性的证书:留数在常数域之外,以及当所有生效的界均被证明时,线性系统显示无留数余项非恰当。

英文摘要

In Part I we extended the structure theorems underlying the Risch--Norman (parallel Risch) method to a simple radical extension $L=K(y)$, $y^m=q$, of a differential field $K=F(t_1,\dots,t_n)$ closed under the derivation. Here we remove the closure hypothesis: the radical may occupy any position in the tower, so that the derivatives of the generators above it involve $y$ --- the setting of Bronstein's algorithm for mixed elementary functions. The working ring is $\cA=\cO[t_{j+1},\dots,t_n]$, the integral closure of $F[t_1,\dots,t_n]$ in $L$: a Krull domain, free over the polynomial ring on Trager's basis, so that all factorisation remains in a unique factorisation domain. The denominator of the derivation is no longer an element but a divisor $\fd_D$ on $\cA$, and the valuation lemma takes the unified form $v_P(Dg)=v_P(g)-(1+v_P(\fd_D))$ at normal height-one primes, subsuming the shifts $\{1,e_P\}$ of Part I; the proof localises and requires no cancellation analysis. Stability of the class group and the unit group, $\Cl(\cA)\cong\Cl(\cO)$ and $\cA^*=\cO^*$, splits the admissible logands into $S$-units of $\cO$ --- computed by the machinery of Part I --- and irreducible polynomials moving in the upper variables, whose residues must be constants. We prove degree bounds in the top variable and describe the resulting algorithm, which --- unlike the classical parallel method, whose failure proves nothing --- returns certificates of non-elementarity in two situations: a residue outside the constant field, and, when every bound in force is proved, a residue-free remainder that the linear system shows to be non-exact.

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