This thesis studies subsemigroups of groups from three perspectives: automatic structures, ordinary semigroup presentations, and Malcev presentaions. [A Malcev presentation is a presentation of a special type for a semigroup that can be embedded into a group. A group-embeddable semigroup is Malcev coherent if all of its finitely generated subsemigroups admit finite Malcev presentations.] The theory of synchronous and asynchronous automatic structures for semigroups is expounded, particularly for group-embeddable semigroups. In particular, automatic semigroups embeddable into groups are shown to inherit many of the pleasant geometric properties of automatic groups. It is proved that group- embeddable automatic semigroups admit finite Malcev presentations, and such presentations can be found effectively. An algorithm is exhibited to test whether an automatic semigroup is a free semigroup. Cancellativity of automatic semigroups is proved to be undecidable. Study is made of several classes of groups: virtually free groups; groups that satisfy semigroup laws (in particular [virtually] nilpotent and [virtually] abelian groups); polycyclic groups; free and direct products of certain groups; and one-relator groups. For each of these classes, the question of Malcev coherence is considered, together with the problems of whether finitely generated subsemigroups are finitely presented or automatic. This study yields closure and containment results regarding the class of Malcev coherent groups. The property of having a finite Malcev presentation is shown to be preserved under finite Rees index extensions and subsemigroups. Other concepts of index are also studied.

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Thesis (Ph. D. in Mathematics)--Vanderbilt University, Aug. 2006. / Title from title screen. Includes bibliographical references.

Made available in DSpace on 2014-07-29T16:02:23Z (GMT). No. of bitstreams: 1 silvio sandro.pdf: 761623 bytes, checksum: 55f280c9ca185766a1ed91423c5edfad (MD5) Previous issue date: 2010-06-28 / The group of weak commutativity for bijection G(H;K;σ) = {H;K|[h;hσ] = 1, for all h H} belongs is defined as the quotient of the free product H * K the normal closure of {[h;hσ] : h belongs to all H} in H * K. In this dissertation, we studied the results obtained in 2009 by Sidka and Oliveira [7] that support the following conjecture: If H,K ~= Zp X...X Zp, then G(H,K,σ)is a p-group. / O grupo de comutatividade fraca por bijeção G(H;K;σ) = {H;K|[h;hσ] = 1, para todo h pertence H} é definido como sendo o quociente do produto livre H * K pelo fecho normal de {[h;hσ] : para todo h pertence H} emH * K. Nessa dissertação, estudamos os resultados obtidos em 2009 por Oliveira e Sidki [7] que suportam a seguinte conjectura: Se H,K ~= Zp X...X Zp, então G(H,K,σ) é um p-grupo.