We study the non-abelian tensor square $G\otimes G$ for the class of groups G that are finitely generated modulo their derived subgroup. In particular, we find conditions on G/G' so that $G\otimes G$ is isomorphic to the direct product of $\nabla(G)$ and the non-abelian exterior square $G\wedge G$. For any group G, we characterize the non-abelian exterior square $G\wedge G$ in terms of a presentation of G. Finally, we apply our results to some classes of groups, such as the classes of free soluble and free nilpotent groups of finite rank, and some classes of finite p-groups.
By using finiteness related result of non-abelian tensor product we prove finiteness conditions for the homotopy groups $π_n(X)$ in terms of the number of tensors. In particular, we establish a quantitative version of the classical Blakers-Massey triad connectivity theorem. Moreover, we study others finiteness conditions and equivalence properties that arise from the non-abelian tensor square. In the end, we give applications to homotopy pushout, especially in the case of Eilenberg-MacLane spaces.
Let $G$ and $H$ be groups that act compatibly on each other. We denote by $[G,H]$ the derivative subgroup of $G$ under $H$. We prove that if the set $\{g^{-1}g^h \mid g \in G, h \in H\}$ has $m$ elements, then the derivative $[G,H]$ is finite with $m$-bounded order. Moreover, we show that if the set of all tensors $T_{\otimes}(G,H) = \{g\otimes h \mid g \in G, h\in H\}$ has $m$ elements, then the non-abelian tensor product $G \otimes H$ is finite with $m$-bounded order. We also examine some finiteness conditions for the non-abelian tensor square of groups.
Schur's theorem and its relation to the closure properties of the non-abelian tensor product
Universidade de Brasilia(巴西利亚大学);Vladimir Chavchanidze Institute of Cybernetics of the Georgian Technical University(格鲁吉亚理工大学弗拉基米尔·查夫奇尼泽网络学研究所);University of Santiago de Compostela(圣地亚哥德孔波斯特拉大学)
On the residual finiteness of the non-abelian tensor square $G \otimes G$, the non-abelian exterior square $G \wedge G$ and the weak commutativity construction $\X(G)$