This thesis is constituted of two articles, both related to Hilbert functions and h-vectors. In the first paper, we deal with h-vectorsof reduced zero-dimensional schemes in the projective plane, and, in particular, with the problem of finding the possible h-vectors for the union of two sets of points of given h-vectors. In the second paper, we generalize the Green’s Hyperplane Restriction Theorem to the case of modules over the polynomial ring. / <p>QC 20131114</p>

In this thesis, we will investigate the rapidly developing eld of computergraphics by giving an insight into the calculations behind the most im-portant topics in perspectives, shading and distance. We will delve intofrequently used shading algorithms and perspective transforms in areas ofcomputer science, architecture and photography, such as pseudo sh-eyelenses and wide-angle lenses.

In 2004 Alexander Postnikov and Boris Shapiro introduced a class of commutative algebras for non-directed graphs. There are two main types of such algebras, algebras of the first type count spanning trees and algebras  of the second type count spanning forests. These algebras have a number of interesting properties including an explicit formula for their Hilbert series. In this thesis we mainly work with the second type of algebras, we discover more properties of the original algebra and construct a few generalizations. In particular we prove that the algebra counting forests depends only on graphical matroid of the graph and converse. Furthermore, its "K-theoretic" filtration reconstructs the whole graph. We introduse $t$ labelled algebras of a graph, their Hilbert series contains complete information about the Tutte polynomial of the initial graph. Finally we introduce similar algebras for hypergraphs. To do this, we define spanning forests and trees of a hypergraph and the corresponding "hypergraphical" matroid.

Octonion algebras are certain algebras with a multiplicative quadratic form. In 2019, Alsaody and Gille showed that, for octonion algebras over unital commutative rings, there is an equivalence between isotopes and isometric quadratic forms. The contravariant equivalence from unital commutative rings to affine schemes, sending a ring to its spectrum, leads us to a question: can the equivalence of isometry and isotopy be generalized to octonion algebras over a (not necessarily affine) scheme? We present the basic definitions and properties of octonion algebras, both over rings and over schemes. Then we show that an isotope of an octonion algebra C over a scheme is isomorphic to a twist by an Aut(C)–torsor. We conclude the thesis by giving an affirmative answer to our question.

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Aritmetik handlar om de fyra räknesätten och innefattar beräkningar och operationer på tal. Algebra är däremot matematikområdet där elever räknar med bokstäver istället för med bara tal. Forskning har visat att när elever arbetar med algebra uppstår vissa missuppfattningar. Syftet med studien var att undersöka vad den matematiska forskningen pekar på som kan vara orsak till att elever har problem med områden av algebra. Denna litteraturstudie baserar sig på matematikdidaktisk forskning. Materialet har analyserats och bearbetats både enskilt och gemensamt utifrån förbestämda urvalskriterier. Det analyserade materialet består av åtta vetenskapliga artiklar, en review-artikel och ett konferensbidrag. I den forskning som har analyserats i studien beskrivs det olika anledningar till missuppfattningar med bokstavssymboler, operationssymboler och prioriteringsregler inom algebra. De två oftast nämnda anledningar är att elever saknar väsentliga kunskaper inom aritmetik och saknar en konceptuell kunskap. Några enstaka texter pekade ut läromedel och lärarens förklaringar som möjliga orsaker till elevers missuppfattningar.

This licentiate thesis consists of two papers on formalization projects using Cubical Agda, a rather new extension of the Agda proof assistant with constructive support for univalence and higher inductive types. The common denominator of the two papers is that they are concerned with structures on types that are sets in the sense of Homotopy Type Theory or Univalent Foundations (HoTT/UF). Univalence gives rise to the so-called structure identity principle (SIP) that plays a prominent role in both papers. This thesis can thus be seen as an investigation into working with “set-level structures” in HoTT/UF. The first paper explains the basics of the SIP implemented in Cubical Agda’s library and is concerned with its application in computer science. In particular, the paper shows how the SIP, when applied to common data structures, can guarantee representation independence internally for certain implementations. These implementations have to be isomorphic in the sense of the SIP. The paper also generalizes the SIP to a relational version that can account for wider classes of implementations. The second paper is concerned with the formalization of affine schemes, a central notion of algebraic geometry. It combines a constructive and point-free approach to schemes with univalence. Schemes have been formalized in several proof assistants by now, but standard textbook presentations often gloss over certain details that in a formalization become very cumbersome to prove. The main result of this paper is that with the help of univalence, or rather the SIP for commutative rings and algebras over a commutative ring, we can directly formalize affine schemes in a way that more closely resembles the standard textbook approach.

In this thesis we explore the topic of resultants, focusing on the resultants of binomial sys-tems. The study aims to provide an introduction to resultants and explore some of the morerecent research on the relationship between cycles in graphs and the resultant of binomialsystems. This will be done by going over some general theory from algebraic geometry suchas polynomials and ideals, in addition to studying the graphs of the binomial systems and thesurrounding theory. The research includes a comprehensive analysis of these graphs and theircycles, leading to findings that the cycles that appear are not restricted in length. This workprovides exploration of a potential extension of the recent research and encourages furtherresearch on the topic.

Representation theory is concerned with the ways of writing elements of abstract algebraic structures as linear transformations of vector spaces. Typical structures amenable to representation theory are groups, associative algebras and Lie algebras. In this thesis we study linear representations of finite groups. The study focuses on character theory and how character theory can be used to extract information from a group. Prior to that, concepts needed to treat character theory, and some of their ramifications, are investigated. The study is based on existing literature, with excessive use of examples to illuminate important aspects. An example treating a class of p-groups is also discussed.

Syftet med denna litteraturstudie var att granska och analysera vad forskning visar beträffande elevers svårigheter för området bråk, samt hur lärare kan underlätta elevers förståelse för bråk i årskurs 4-6. I litteraturstudien har databassökningar gjorts via UniSearch, ERIC, MathEduc och Google Scholar. Även manuella sökningar har använts. Bråk tonas ned i dagens undervisning och resultat från TIMSS och PISA visar att bråk är ett, för elever såväl som lärare, problematiskt område i matematiken. Forskare framhåller bland annat elevers svårigheter för täljaren och nämnarens innebörd, samt jämförelse och beräkning av bråkuttryck. Vidare framhäver forskare att lärare med bland annat diskussioner i klassrummet, praktiskt material, samt en verklighetsanknuten och elevcentrerad bråkundervisning främjar elevers inlärning. Resultaten visar dock att forskare inte är eniga vad gäller de svårigheter elever har på området bråk.