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Realizable ranks of joins and intersections of subgroups in free groups
International Journal of Algebra and Computation ( IF 0.8 ) Pub Date : 2019-11-08 , DOI: 10.1142/s0218196720500149
Ignat Soroko 1
Affiliation  

The famous Hanna Neumann Conjecture (now the Friedman–Mineyev theorem) gives an upper bound for the ranks of the intersection of arbitrary subgroups [Formula: see text] and [Formula: see text] of a non-abelian free group. It is an interesting question to “quantify” this bound with respect to the rank of [Formula: see text], the subgroup generated by [Formula: see text] and [Formula: see text]. We describe a set of realizable values [Formula: see text] for arbitrary [Formula: see text], [Formula: see text], and conjecture that this locus is complete. We study the combinatorial structure of the topological pushout of the core graphs for [Formula: see text] and [Formula: see text] with the help of graphs introduced by Dicks in the context of his Amalgamated Graph Conjecture. This allows us to show that certain conditions on ranks of [Formula: see text], [Formula: see text] are not realizable, thus resolving the remaining open case [Formula: see text] of Guzman’s “Group-Theoretic Conjecture” in the affirmative. This in turn implies the validity of the corresponding “Geometric Conjecture” on hyperbolic 3-manifolds with a 6-free fundamental group. Finally, we prove the main conjecture describing the locus of realizable values for the case when [Formula: see text].

中文翻译:

自由组中子组的可实现的连接和交集等级

著名的汉纳诺依曼猜想(现在的弗里德曼-米涅耶夫定理)给出了一个非阿贝尔自由群的任意子群 [公式:见正文] 和 [公式:见正文] 的交集等级的上限。关于[公式:参见文本]的等级“量化”这个界限是一个有趣的问题,[公式:参见文本]和[公式:参见文本]生成的子组。我们为任意[公式:见文本]、[公式:见文本]描述了一组可实现的值[公式:见文本],并推测该轨迹是完整的。我们借助 Dicks 在他的融合图猜想中引入的图,研究了 [公式:见文本] 和 [公式:见文本] 的核心图的拓扑推出的组合结构。这使我们能够证明 [公式:见文]、[公式:见文]是不可实现的,从而肯定地解决了古兹曼的“群论猜想”的剩余未决情况[公式:见文]。这反过来又暗示了相应的“几何猜想”在具有 6 个自由基群的双曲 3 流形上的有效性。最后,我们证明了描述可实现值轨迹的主要猜想[公式:见正文]。
更新日期:2019-11-08
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