ABSTRACT
This thesis assembles two papers in mathematics and two papers in mathematics education.
In the mathematics part, representation theory is practised. Two Clebsch-Gordan type
problems are addressed. The original problem concerns the decomposition of the tensor
product of two finite dimensional, irreducible highest way representations of GLC
(n). This
problem is known to be equivalent with the characterisation of the eigenvalues of the sum
of two Hermitian matrices. In this thesis, the method of moment maps and coadjoint
orbits are used to find equivalence between the eigenvalue problem for skew-symmetric
matrices and the tensor product decomposition in the case of SOC
(2k). In addition, some
irreducible, infinite dimensional, unitary highest weight representations of glC
(n + 1) are
determined.
In the mathematics education part a framework is developed, offering a language and
graphical tool for representing the exercising of competence in mathematical practices. The
development sets out from another framework, where competence is defined in terms of
mastery. Adjustments are made in order to increase the coherence of the framework, to
relate the constructs to contemporary research and to enable analysis of the exercising of
competence. These modifications result in two orthogonal sets of essential aspects of mathematical
competence: five competencies and two aspects. The five competencies reflect
different constituents of mathematical practice: representations, procedures, connections,
reasoning and communication. The two aspects evince two different modes of the competencies:
the productive and the analytic. The operationalisation of the framework gives rise
to an analysis guide and a competency graph.
The framework is applied to two sets of empirical data. In the first study, young children’s
exercising of competencies in handling whole numbers is analysed. The results show
that the analytical tools are able to explain this mathematical practice from several angles:
in relation to a specific concept, in a certain activity and how different representations may
pervade procedures and interaction. The second study describes university students’ exercising
of competencies in a proving activity. The findings reveal that, while reasoning and
the analytic aspect are significant in proving, the other competencies and the productive
aspect play important roles as well. Combined, the two studies show that the framework
have explanatory power for various mathematical practices. In light of this framework, this
thesis exercises both aspects of mathematical competence: the productive aspect in representation
theory and the analytic aspect in the development of the framework.