MARCH 1999
nEllipses and the Minimum Distance Sum Problem
by Junpei Sekino
[email protected]
Given n points in a plane, which we call foci, an nellipse is the locus of points in the plane the sum of whose distances from the foci is a constant. Like circles (1ellipses) and ellipses (2ellipses), nellipses are Jordan curves with convex interiors but come in a greater variety of shapes such as crosssections of eggs and filberts; some of them even resemble contours of human faces, symmetric or asymmetric. After illustrating some of these figures (computer generated), we turn our attention to the critical points of the distance sum function whose contours are nellipses. We show that a critical point is nondegenerate if and only if the foci are noncollinear, and demonstrate that a nondegenerate critical point not only yields a unique point minimizing the distance sum function but also possesses a geometrically appealing property. The paper concludes with an optimization problem and a suggestion for a further generalization of an ellipse to an nellipse with weights.
The Bieberbach Conjecture and Milin's Functionals
by Arcadii Z. Grinshpan
[email protected]
The Bieberbach conjecture (1916) for the Taylor coefficients of onetoone analytic functions is one of the most famous and inspirational problems of mathematics. This conjecture remained open for nearly 70 years until in 1984 L. de Branges proved a stronger conjecture for certain logarithmic functionals proposed by I. M. Milin in 1971.
de Branges' approach was based on Loewner's parametric method (1923), a classic tool in geometric function theory, but it involved other fields of mathematics as well. Simplifications made by several authors during 19841997 have led to the present proof, which is now accessible to many readers.
Decision Making: A Golden Rule
by Dimitris A. Sardelis and Theodoros M. Valahas
[email protected]
This article is an educational exposition of a classical optimalstopping problem, the dowry problem. Its solution is presented by building on easily understandable special cases. A pattern of optimal strategies emerges, which is ultimately expressed by general conditions that lead to the (1/e) golden decision rule.
A Tale of Two Integrals
by Vilmos Totik
[email protected]
In the paper several approaches are presented to the following simplelooking but highly nontrivial combinatorialanalysis problem: [0,1] whose integrals ove [0,1] are both equal to 1. Show that there is some interval I [0,1] such that the integrals of f and g over I are both equal to 1/2. This problem is equivalent to the following problem without integrals: On a blackjack machine one can win or lose one dollar at a time. Suppose two players playing once per minute during a period find that eventually both of them win exactly 2N dollars. Show that there was a time interval during which both of them won exactly N dollars.
Six solutions are presented that are based on other combinatorial or geometrical/topological results. These are:

the BorsukUlam antipodal theorem on continuous mappings of spheres;

the mountain climbing problem on two climbers staying always at the same altitude;

the chord theorem for parallel chords of planar curves;

the chess kingmoving theorem on king walks on cells of the same colour;

the winding number theorem for vector fields;

the Jordan curve theorem on components of simple curves.
A Mathematical Excursion: From the ThreeDoor Problem to a CantorType Set
by Jaume Paradís, Pelegrí Viader, and Lluís Bibiloni
[email protected], [email protected], [email protected]
Can you imagine a connection between the wellknown threedoor problemalso known as the Monty Hall problemand a set with a complex structure like Cantor's set? We offer a generalization of the threedoor problem, the nbox problem, whose solution provides us with a system for real number representation, Pierce expansions. Through these expansions we get a new enumeration of the positive rationals and also a Cantortype set containing only transcendental numbers.
NOTES
An Inequality Relating the Circumradius and Diameter of
TwoDimensional LatticePointFree Convex Bodies
by Poh Wah Awyong
[email protected]
Cutting a Polyomino into Triangles of Equal Areas
by Sherman K. Stein
[email protected]
A Short Proof of Turaacute;nÕs Theorem
by William Staton
[email protected]
A Characterization of the Set of Points of Continuity of a Real Function
by Sung Soo Kim
[email protected]
THE EVOLUTION OF...
The Literal Calculus of Vieacute;te and Descartes
by I. G. Bashmakova and G. S. Smirnova
PROBLEMS AND SOLUTIONS
REVIEWS
An Accompaniment to Higher Mathematics
By George R. Exner
Journey Into Mathemtics: An Introduction to Proofs
By Joseph Rotman
Mathematical Thinking: Problem Solving and Proofs
By John P. D'Angelo and Douglas B. West
Reviewed by Joseph H. Silverman
[email protected]
The Social Life of Numbers: A Quechua Ontology of Numbers
and Philosophy of Arithmetic
By Gary Urton
Reviewed by John Meier and Trisha Thorme
[email protected], [email protected]
TELEGRAPHIC REVIEWS
EDITOR'S ENDNOTES