November 2010
Teaching Research: Encouraging Discoveries
By: Francis Edward Su
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What does it take to turn a learner into a discoverer? Or to turn a teacher into a coadventurer? A handful of experiencesÂ—from teaching a middleschool math class to doing research with undergraduatesÂ—have changed the way that I would answer these questions. Some of the lessons I've learned have surprised me.
Julius and Julia: Mastering the Art of the Schwarz Lemma
By: Harold P. Boas
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This article discusses classical versions of the Schwarz lemma at the boundary of the unit disk in the complex plane. The exposition includes commentary on the history, the mathematics, and the applications.
Fermat’s Spiral and the Line Between Yin and Yang
By: Taras Banakh, Oleg Verbitsky, and Yaroslav Vorobets
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Let D denote a disk of unit area. We call a set perfect if it has measure 1/2 and, with respect to any reflection symmetry of D, the maximal symmetric subset of A has measure 1/4. We call a curve in D a yinyang line if

splits D into two congruent perfect sets,

crosses each concentric circle of D twice,

crosses each radius of D once.
We prove that Fermat’s spiral is the unique yinyang line in the class of smooth curves
algebraic in polar coordinates.
Analysis with Ultrasmall Numbers
By: Karel Hrbacek, Olivier Lessmann, and Richard O’Donovan
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We develop a contextbased theory of ultrasmall (infinitesimal) and ultralarge real numbers from a few simple principles, and present some examples of their use in analysis. In this theory, perhaps for the first time, definitions and arguments involving infinitesimals can be presented in a style that is both as informal and as rigorous as is customary in standard textbooks of real analysis.
Notes
Irreducible Cubics Modulo Five
By: Hendrik Lenstra
Finite fields are finite, and they are fields, and as a result one can combine algebraic arguments with counting arguments in their study. This was illustrated in a lecture given at the 2009 April Fools’ meeting of the Leiden bachelor seminar. Here is the text of that lecture.
A Short Proof of Combinatorial Nullstellensatz
By: Mateusz MichaÅ‚ek
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In this note we give a short, direct proof of the combinatorial Nullstellensatz.
A Continuous Bijection from onto a Subset of Whose Inverse Is Everywhere Discontinuous
By: Sam H. Creswell
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There is a continuous bijection from onto a subset of whose inverse is everywhere discontinuous.
On a Question of Connes and Zagier Regarding Parallelograms Inscribed in a Pair of Confocal Ellipses
By: Nicolae Anghel
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It is shown that a pair of nested concentric ovals has the property that each point on either one of the ovals is a vertex of exactly one inscribed parallelogram of maximal perimeter if and only if the joint Monge orthoptic curve of the ovals is a circle. This gives an answer to a question posed by Connes and Zagier in the note A property of parallelograms inscribed in ellipses, which appeared in the American Mathematical Monthly in 2007.
A Streamlined Proof of an Essential Calculus Fact
By: Stephen M. Walk
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We present a short, classroomfriendly proof of a standard theorem of calculus: continuity on an interval implies Riemannintegrability on that interval. Reviews
Statistical Models: Theory and Practice (Revised Edition).
By: David A. Freedman
Reviewed by: Rebecca F. Goldin
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