A morphism $\sigma$ is \emph{(strongly) unambiguous} with respect to a word $\alpha$ if there is no other morphism $\tau$ that maps $\alpha$ to the same image as $\sigma$. Moreover, $\sigma$ is said to be \emph{weakly unambiguous} with respect to a word $\alpha$ if $\sigma$ is the only \emph{nonerasing} morphism that can map $\alpha$ to $\sigma(\alpha)$, i.\,e., there does not exist any other nonerasing morphism $\tau$ satisfying $\tau(\alpha) = \sigma(\alpha)$. In the first main part of the present thesis, we wish to characterise those words with respect to which there exists a weakly unambiguous \emph{length-increasing} morphism that maps a word to an image that is strictly longer than the word. Our main result is a compact characterisation that holds for all morphisms with ternary or larger target alphabets. We also comprehensively describe those words that have a weakly unambiguous length-increasing morphism with a unary target alphabet, but we have to leave the problem open for binary alphabets, where we can merely give some non-characteristic conditions. \par The second main part of the present thesis studies the question of whether, for any given word, there exists a strongly unambiguous \emph{1-uniform} morphism, i.\,e., a morphism that maps every letter in the word to an image of length $1$. This problem shows some connections to previous research on \emph{fixed points} of nontrivial morphisms, i.\,e., those words $\alpha$ for which there is a morphism $\phi$ satisfying $\phi(\alpha) = \alpha$ and, for a symbol $x$ in $\alpha$, $\phi(x) \neq x$. Therefore, we can expand our examination of the existence of unambiguous morphisms to a discussion of the question of whether we can reduce the number of different symbols in a word that is not a fixed point such that the resulting word is again not a fixed point. This problem is quite similar to the setting of Billaud's Conjecture, the correctness of which we prove for a special case.

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Thesis (Ph. D.)--State University of New York at Binghamton, Department of Systems Science and Industrial Engineering, Thomas J. Watson School of Engineering and Applied Science, 2007. / Includes bibliographical references.

Thesis (Ph. D.)--Rochester Institute of Technology, 1993. / Typescript. Includes bibliographical references (leaves 156-169).

In this bachelor’s thesis an introduction to the fundamentals of algebraic geometry is given. Some concepts in algebraic geometry are introduced such as Spec of a ring and Proj of a graded ring and several results related to these are either proven or stated. Special focus is directed towards defining the so called ”Hilbert scheme” which is the main topic in a lot of modern algebraic geometry research.

Fix R = k[[x]]. Let Q_n be the category whose objects are ((M₁,...,M_n),(f₁,...,f_n-1)) where each M_i is a free R-module and f_i:M_i⟶M_i+1 for each i=1,...,n-1, and in which the morphisms are the obvious ones. Let β_n be the full subcategory of Ω_n in which each map f_i is a monomorphism whose cokernel is a torsion module. It is shown that there is a full dense functor Ω_n⟶β_n. If X is an object of β_n, we say that X <u>diagonalizes</u> if X is isomorphic to a direct sum of objects ((M₁,...,M_n),(f₁,...,f_n-1)) in which each M_i is of rank one. We establish an algorithm which diagonalizes any diagonalizable object X of β_n, and which fails only in case X is not diagonalizable. Let Λ be an artin algebra of finite type. We prove that for a fixed C in mod(Λ) there are only finitely many modules A in mod(Λ) (up to isomorphism) for which a short exact sequence of the form 0⟶A⟶B⟶C⟶0 is indecomposable. / Ph. D. / incomplete_metadata

In this thesis we present the deformation theory of Lie groupoid morphisms, Lie subgroupoids and symplectic groupoids. The corresponding deformation complexes governing such deformations are defined and used to investigate a Moser argument in each of these contexts. We also apply this theory to the case of Lie group morphisms and Lie subgroups, obtaining rigidity results of these structures. Moreover, in the case of symplectic groupoids, we define a map between the differentiable and deformation cohomology of the underlying groupoid, which is regarded as the global counterpart of a map $i$ defined by Crainic and Moerdijk (2004) which relates the (Poisson) cohomology of the Poisson structure on the base $M$ of the groupoid to the deformation cohomology of the Lie algebroid $T^{*}M$ associated to it. / Nesta tese apresentamos a teoria de deformação de morfismos de grupoides de Lie, subgrupoides de Lie e grupoides simpléticos, definimos os correspondentes complexos de deformação que controlam as deformações destas estruturas, e usamos estes complexos para desenvolver o argumento de Moser em cada um destes contextos. Também aplicamos esta teoria ao caso de morfismos de grupos de Lie e subgrupos de Lie obtendo resultados de rigidez de tais estruturas. Ademais, no caso de grupoides simpléticos, definimos uma função entre a cohomologia diferenciável e a cohomologia de deformação do grupoide, que é interpretada como o análogo global da aplicação $i$ definida por Crainic e Moerdijk (2004) que relaciona a cohomologia de Poisson da estrutura de Poisson induzida na base $M$ do grupoide com a cohomologia de deformação do algebroide de Lie $T^{*}M$ associado à estrutura de Poisson.

Nesta tese estudamos o conceito de grau de um morfismo irredutível em ${m mod}A$ relacionado ao conceito de teoria de partições pós-projetiva e pré-injetiva de uma álgebra de artin $A$. Introduzimos o conceito de grau de um morfismo irredutível em relação a uma categoria ${\\mathfrak D}$ de ${m ind}A$ e estudamos o caso em que ${\\mathfrak D}$ é um elemento da partição ${\\bf P_0}, \\cdots, {\\bf P_{\\infty}}$. Dentro do contexto de grau de um irredutível em relação a uma subcategoria resolvemos um problema proposto por Chaio, Le meur e Trepode em \\cite. Utilizando as partições pós-projetiva e pré-injetiva obtemos outra demonstração para a caracterização de álgebras de tipo finito obtida em \\cite e obtemos uma caracterização semelhante para subcategorias de módulos $\\Delta$-bons de tipo finito de ${m mod}A$ tal que $A$ é uma álgebra quasi-hereditária. Também utilizamos a teoria de partições para provar que, dada uma álgebra quasi-hereditária $A$ e ${\\cal F}(\\Delta) \\subseteq {m mod}A$, se $({m rad}_{\\Delta}^{\\infty})^2=0$ então ${\\cal F}(\\Delta)$ é de tipo finito. / In this thesis we analyse the concept of the degree of an irreducible morphism associated to the theory of postprojective and preinjective partitions. We introduce the idea of the degree of an irreducible morphism with respect to a subcategory ${\\mathfrak D}$ and we study the case in which ${\\mathfrak D}$ is an element of the postprojective partition ${\\bf P_0}, \\cdots, {\\bf P_{\\infty}}$. By using the concept of the degree of an irreducible morphism with respect to a subcategory ${\\mathfrak D}$ we present a solution to a problem recently proposed by Chaio, Le Meur and Trepode in \\cite. We also use the theory of postprojective and preprojective partitions to give another proof to the characterization of finite type algebras obtained by Chaio and Liu in \\cite and we apply similar techniques to obtain a characterization of finite type ${\\cal F}(\\Delta)$ subcategories where ${\\cal F}(\\Delta)$ is the subcategory of $\\Delta$-good modules of the category of finitely generated modules over a quasi-hereditary algebra. We also prove that given a quasi-hereditary algebra $A$ and ${\\cal F}(\\Delta) \\subseteq {m mod}A$, if $({m rad}_{\\Delta}^{\\infty})^2=0$ then ${\\cal F}(\\Delta)$ is of finite type.

Nesta tese estudamos o conceito de grau de um morfismo irredutível em ${m mod}A$ relacionado ao conceito de teoria de partições pós-projetiva e pré-injetiva de uma álgebra de artin $A$. Introduzimos o conceito de grau de um morfismo irredutível em relação a uma categoria ${\\mathfrak D}$ de ${m ind}A$ e estudamos o caso em que ${\\mathfrak D}$ é um elemento da partição ${\\bf P_0}, \\cdots, {\\bf P_{\\infty}}$. Dentro do contexto de grau de um irredutível em relação a uma subcategoria resolvemos um problema proposto por Chaio, Le meur e Trepode em \\cite. Utilizando as partições pós-projetiva e pré-injetiva obtemos outra demonstração para a caracterização de álgebras de tipo finito obtida em \\cite e obtemos uma caracterização semelhante para subcategorias de módulos $\\Delta$-bons de tipo finito de ${m mod}A$ tal que $A$ é uma álgebra quasi-hereditária. Também utilizamos a teoria de partições para provar que, dada uma álgebra quasi-hereditária $A$ e ${\\cal F}(\\Delta) \\subseteq {m mod}A$, se $({m rad}_{\\Delta}^{\\infty})^2=0$ então ${\\cal F}(\\Delta)$ é de tipo finito. / In this thesis we analyse the concept of the degree of an irreducible morphism associated to the theory of postprojective and preinjective partitions. We introduce the idea of the degree of an irreducible morphism with respect to a subcategory ${\\mathfrak D}$ and we study the case in which ${\\mathfrak D}$ is an element of the postprojective partition ${\\bf P_0}, \\cdots, {\\bf P_{\\infty}}$. By using the concept of the degree of an irreducible morphism with respect to a subcategory ${\\mathfrak D}$ we present a solution to a problem recently proposed by Chaio, Le Meur and Trepode in \\cite. We also use the theory of postprojective and preprojective partitions to give another proof to the characterization of finite type algebras obtained by Chaio and Liu in \\cite and we apply similar techniques to obtain a characterization of finite type ${\\cal F}(\\Delta)$ subcategories where ${\\cal F}(\\Delta)$ is the subcategory of $\\Delta$-good modules of the category of finitely generated modules over a quasi-hereditary algebra. We also prove that given a quasi-hereditary algebra $A$ and ${\\cal F}(\\Delta) \\subseteq {m mod}A$, if $({m rad}_{\\Delta}^{\\infty})^2=0$ then ${\\cal F}(\\Delta)$ is of finite type.

Algebraic theories and algebraic categories offer an innovative and revelatory description of the syntax and the semantics. An algebraic theory is a concrete mathematical object -- the concept -- namely a set of variables together with formal symbols and equalities between these terms; stated otherwise, an algebraic theory is a small category with finite products. An algebra or model of the theory is a set-theoretical interpretation -- a possible meaning -- or, more categorically, a finite product-preserving functor from the theory into the category of sets. We call the category of models of an algebraic theory an algebraic category. By generalising the theory we do generalise the models. This concept is the fascinating aspect of the subject and the reference point of our project. We are interested in the study of categories of models. We pursue our task by considering models of different theories and by investigating the corresponding categories of models they constitute. We analyse localizations (namely, fully faithful right adjoint functors whose left adjoint preserves finite limits) of algebraic categories and localizations of presheaf categories. These are still categories of models of the corresponding theory. We provide a classification of localizations and a classification of geometric morphisms (namely, functors together with a finite limit-preserving left adjoint), in both the presheaf and the algebraic context.