Hans-Georg Steiner: a life dedicated to the development of didactics of mathematics as a scientific discipline

In our introductory paper to this special issue we follow two goals. First of all, we take on the challenge to give an account of more than 40 years of academic work by one of the leading members of our discipline by looking at Hans Georg Steiner’s contributions to the development of didactics of mathematics as a scientific discipline in Germany as well as internationally. Therefore, we try to highlight major research interests, publications and conferences during his early years in Münster, Karlsruhe and Bayreuth as well as during the 20 years at the IDM in Bielefeld. Closely linked to these periods of this life and work are specific research interests, professional contacts and friendships. Hence, the second goal of our paper is to emphasise Hans-Georg Steiner’s relationships with national and international colleagues (many of whom became friends) and their shared interests and collaborations in the development of mathematics education through a selection of invited papers that address different stages and professional foci in the life of Hans-Georg Steiner. These papers are organised in four sections: (1) Revisiting the New Math reform, (2) Developing specific research domains in didactics of mathematics, (3) Discussing theories of mathematics education (TME), and (4) Reflecting on goals and results of mathematics education.     

The development of mathematics textbooks: historical reflections from a personal perspective

The paper begins with a reflective, historical overview of the role and development of textbooks and research into their use. Since much of the writing is based on personal experience, there is an obvious UK bias, although experiences there were not dissimilar to what was happening in many other countries at that time. Particular attention is then paid to comparative studies: the difficulties they pose and what can be usefully gained from them. To help in this latter aspect, an attempt is made to distinguish what would appear to be key features of textbooks (or, indeed, other educational materials) which might be assessed in such a study and, in particular, the vital role of the exercises to be found in them.     

Exemplary mathematics lessons: a view from the West

Cross-cultural comparative research provides a powerful means of achieving better understanding of one’s own practice. This article contrasts exemplary mathematics teaching, as highlighted in this special issue on its practice and development in East Asia, with the increasing emphasis on effective teaching in the West. It provides an overview of the papers in this issue and examines the similarities and differences between what is seen as exemplary practice and the ways in which its development is supported in the educational systems represented. It attempts to identify some of the cultural factors that influence our understanding of what constitutes exemplary practice and the possibilities for its development in the East and the West.     

Solitons from a direct point of view: padeons

A systematic approach to soliton interaction is presented in terms of a particular class of solitary waves (padeons) which are linear fractions with respect to the nonlinearity parameter ϵ. A straightforward generalization of the padeon to higher order rational fractions (multipadeon) yields a natural ansatz for N-soliton solutions. This ansatz produces multisoliton formulas in terms of an ‘interaction matrix’ A. The structure of the matrix gives some insight into the hidden IST-properties of a familiar set of ‘integrable’ equations (KdV, Boussinesq, MKdV, sine-Gordon, nonlinear Schrödinger). The analysis suggests a ‘padeon’ working definition of the soliton, leading to an explicit set of necessary conditions on the padeon equation.     

A proportional view: The mathematics of James Glenie (1750–1817)

The mathematical work of James Glenie (1750–1817) was published at irregular intervals during a turbulent life. His ideas, mostly deriving from his time as an Assistant in Mathematics at St Andrews University in Scotland, were developed intermittently over a period of thirty-seven years. His mathematical achievements, underestimated by previous historians, were deeply rooted in Euclidean geometry and his own generalized theory of proportion. Among them are many new geometrical constructions and proofs, a novel demonstration of the binomial theorem, and an alternative approach to the differential calculus.     

A history of topological and analytical semigroups: a personal view

A retrospective of the historical development of a topological and analytical theory of semigroups is given from a personal vantage point. It begins with SOPHUS LIE who from about 1880 onward dealt with semigroups by default, having no clear concept of a group at first. The algebraic theory of semigroups emerged in the first half of the 20th century, but its topological counterpart emancipated itself as late as in the second half. I shall comment on the genesis of a theory of compact topological semigroups in the fifties under the influence of A. D. WALLACE. These semigroups came into focus at about the same time E. S. LYAPIN raised the important issue of magnifying elements, thereby discovering the bicyclic semigroup wherever those exist. Compact topological semigroups, however, cannot contain bicyclic semigroups; this has interesting consequences. - Around 1970 D. S. SCOTT discovered what he called continuous lattices and what nowadays, in more general form, is called domains, whileJ. D. LAWSON drew semigroup theoreticians' attention to a very natural class of compact semilattices having enough homomorphisms into the unit interval semilattice. The class of continuous lattices agrees with the class of Lawson semilattices. It generates a network of applications in theoretical computer science under the name "domain theory". - A hundred years after SOPHUS LIE's differentiable groups and semigroups, attention returned back to semigroups and Lie theory. Lie semigroup theory, initiated by E. B. VINBERG, G. I. OLSHANSKY, J. D. LAWSON and the author among others, infused a strong geometric and analytical flavor into topological semigroup theory and generated a new lines of application of semigroup theory such as in geometric control theory, and in the area of unitary representation theory of Lie groups, particulary in the area of holomorphic extensions of unitary representations. A respectable number of mongraphs and collections have been and are being written in this field.     

Displacement interpolations from a Hamiltonian point of view

One of the most well-known results in the theory of optimal transportation is the equivalence between the convexity of the entropy functional with respect to the Riemannian Wasserstein metric and the Ricci curvature lower bound of the underlying Riemannian manifold. There are also generalizations of this result to the Finsler manifolds and manifolds with a Ricci flow background. In this paper, we study displacement interpolations from the point of view of Hamiltonian systems and give a unifying approach to the above mentioned results.     

Generalized quadrangles from a local point of view

In this lecture, I will survey several recent results in the local theory of generalized quadrangles. Starting with a short introduction to the global automorphism theory, I will motivate as such the local viewpoint, and overview some of the most important local properties which are investigated nowadays. Recent results on skew translation quadrangles and forms will be described, including a solution of a question of Payne which generalizes work of Havas et?al. (Finite geometries, groups, and computation, 2006; Adv Geom 26:389?C396, 2006), and then I will mention parts of a classification of skew translation quadrangles which is being prepared by the author. Finally, I will consider conditions which are both global and local.     

Structured continua from a lagrangian point of view

Sunto In questo lavoro si studiano le ipersuperfici di bigrado (p, 2)in P ¹×P ^m ,m3m dispari p1.Tali ipersuperfici per p=1si presentanto in modo naturale nello studio del problema di Torelli per le intersezioni complete di due quadriche trasverse in P ^m .Viene analizzata la loro struttura e dimostrato che per p2il Teorema di Torelli non vale per tali ipersuperfici mentre vale per p=1 (Turin).

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Partially supported by a C.N.R. fellowship at the University of Georgia, Athens, Georgia.     

Toward a scientific and personal biography of Tullio Levi-Civita (1873–1941)

Tullio Levi-Civita was one of the most important Italian mathematicians of the first part of the 20th century, contributing significantly to a number of research fields in mathematics and physics. In addition, he was involved in the social and political life of his time and suffered severe political and racial persecution during the period of Fascism. He tried repeatedly and in several cases successfully to help colleagues and students who were victims of anti-Semitism in Italy and Germany. His scientific and private life is well documented in the letters and documents contained in his Archive. The authors' aim is to illustrate the events of his life by means of his large and remarkable correspondence.     

Compressed sensing from a harmonic analysis point of view

This paper gives an easy and purely harmonic analysis approach of the compressed sensing theory of Candès, Romberg and Tao. It contains an application to the determination of a lacunary trigonometric series whose sum is known on an interval, and a critical appreciation of this application.     

Fuzzy sets: A topos-logical point of view

Bénabou deduction-categories are defined, with a set of additional assumptions that define categories with formal finite limits (resp. formal regular categories, formal logoi, formal topoi). They are shown to be generalized structures in which higher-order many-sorted languages can be realized. The corresponding Gentzen-type higher-order calculus of sequents is explicited and the soundness theorem is formulated. A construction is given, which associates to each deduction category with formal properties a real category with the corresponding real properties, in a universal way. The corresponding sounddess and completeness properties are formulated for the real categories thus obtained. Fuzzy sets, as generalized by Goguen are introduced, considered as the objects of a category Fuz(H), which turns out to be the real category associated to a very simple formal topos, and thus to be itself a topos: furthermore this is proved to be a Grothendieck topos which is a strictly full epireflective subcategory of Higgs' category of ‘H-valued sets’. Topoi are proposed as generalized fuzzy sets, and deductio0-categories as generalized² fuzzy sets. Some related topics such as Arbib-Manes fuzzy theories, probability, many-valued and fuzzy logics, intensional logic are very briefly touched upon.     

Modern thermodynamics as a branch of mathematics (mathematical physics)

In the paper, it is proved that, if f(x₁,..., x_n)g(y₁,..., y_m) is a multilinear central polynomial for a verbally prime T-ideal Γ over a field of arbitrary characteristic, then both polynomials f(x₁,..., x_n) and g(y₁,..., y_m) are central for Γ.     

The Gibbs' phenomenon from a signal processing point of view

Recently, Fay and Kloppers gave two proofs to show that the well-known Gibbs' phenomenon for Fourier series at a jump discontinuity depends only on the size of the jump and is a multiple of the integral 1/π ∫₀ ^π (sin x / x) dx. We give another proof, based upon low-pass filtering of the Fourier transform, that uses the observation that a truncated Fourier series for a function ? (x) is ‘very nearly’ equal to the convolution integral 1/π ∫ _-∞ ^+∞ ? (x - t)(sin nt / t) dt.     

The SIR epidemic model from a PDE point of view

We present a derivation of the classical Susceptible-Infected-Removed (SIR) and Susceptible-Infected-Removed-Susceptible (SIRS) models through a mean-field approximation from a discrete version of SIR(S). We then obtain a hyperbolic forward Kolmogorov equation, and show that its projected characteristics recover the standard SIR(S) model. Moreover, for the SIRS model, we show that the long time limit of the SIRS model will be a Dirac measure supported on the corresponding isolated equilibria. For the SIR model, we show that the long time limit is a Radon measure supported in a segment of nonisolated equilibria.