 Proofs in Mathematics  Interactive Mathematics Miscellany and Puzzles, Alexander Bogomolny
A discussion of the value of proofs in the classroom, followed by a collection of proofs classified as either simple or charming. Simple proofs: Number of vowels in a Lewis Carroll game; Pigeonhole Principle; Number of X's and O's; Coloring points in
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 Proofs Wiki  Brunner Nathan
A communitybased collection of definitions, proofs, and theorems. The Proofs Wiki composition interface supports LaTeX and tooltips.
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 Proofs Without Words  Cut the Knot!, Alexander Bogomolny
Martin Gardner wrote, "There is no more effective aid in understanding certain algebraic identities than a good diagram. One should, of course, know how to manipulate algebraic symbols to obtain proofs, but in many cases a dull proof can be supplemented
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 Proof Techniques (Analysis Webnotes)  John Lindsay Orr; Dept. of Mathematics & Statistics, Univ. of NebraskaLincoln
Techniques of writing proofs for: Showing two sets are equal; Showing a set is closed; How to show a sequence converges; and How to use a convergent sequence (to prove other things).
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 A Proof that e is Irrational  Isaac Reed
A proof by contradiction that relies on the expression of e as a power series.
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 A Proof That e is Transcendental  Travis Kidd
A proof by contradiction, adapted from Klein, Famous Problems (New York: Chelsea Publishing Company, 1962).
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 Proof: The Sum of Prime Twins is Divisible by 12  Mathematics Dept., College of Marin
Prime twins are prime numbers that are two numbers apart. For example 41 and 43 are prime twins. Can you PROVE that the sum of prime twins is divisible by 12?
(This proof doesn't work for the prime twins 3 and 5.)
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 ProofWiki  Matt Westwood
ProofWiki is an online compendium of mathematical proofs. Those interested in adding to the work are urged to create an account and contribute.
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 Properties of Dice  Klaus Mogensen
An essay on Proper Dice (illustrated) and Dice Roll Probabilities.
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 Prophet of Chaos  Ivars Peterson (MathTrek)
"'...it may happen that small differences in the initial conditions produce very great ones in the final phenomena. A small error in the former will produce an enormous error in the latter. Prediction becomes impossible, and we have the fortuitous phenomenon.'
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 À propos d'Alexandre Grothendieck  Eric Dumas
Une entrevue avec Jean Giraud, avec des références.
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 Proudnerd.com  Heather Sable
"For the selfassured nerd": humorous tshirts, long sleeve tshirts, women's tshirts, sweatshirts, hooded sweatshirts, boxer shorts, hats and caps, bags and backpacks, mugs and cups, mousepads, apparel for kids, babies, and toddlers, and more. Solve
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 The ProvenMath Project  Michal Ryszard Wojcik and Michal Stanislaw Wojcik
Proofs of the Fundamental Theorem of Algebra, the theorem about integration by change of variables for realvalued functions of nvariables, a derivation of Zorn's Lemma, and others. The site renders axioms and derives proofs using only ASCII characters.
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 PR Probability Theory (Front for the Mathematics ArXiv)  Univ. of California, Davis
Probability Theory preprints, from the U.C. Davis front end for the xxx.lanl.gov ePrint archive, a major site for mathematics preprints that has incorporated many formerly independent specialist archives. Search by keyword or browse by topic.
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 PseudoDifferential Operators  Mark S. Joshi; Cambridge University, UK
Lecture notes in postscript, PDF, and dvi formats covering a first year graduate course on pseudodifferential operators. The calculus on manifolds is developed and applied to prove propagation of singularities and the Hodge decomposition theorem. Problems
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 P.T. Chang
Articles by this math professor from the University of Alaska Anchorage's MatSu College include "The Ostentatious World of Algebra," "InService Training for the Math Teacher of the 21st Century," and "Retesting in a College Remedial Mathematics Course."
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 PTC: Product Lifecycle Management Software  Parametric Technology Corporation
PTC acquired MathSoft, developer of Mathcad and other software for math, science and engineering for business, research, academic and government markets. They also market Pro/ENGINEER, Windchill, Arbortext, ProductView, CoCreate, and InSight.
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 Publications and Research Tools (AMS)  American Mathematical Society
The AMS research and publishing services include MathSciNet and the AMS Electronic Journals. Research tools for mathematicians include Mathematical Reviews Author Lookup, Institution Codes and Addresses, Serials Abbreviations; the AMS Preprint Server,
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 Publications  Douglas N. Arnold; Institute for Mathematics and its Applications
Most of Arnold's papers written since the late 1980s are available in PostScript, TeX DVI or plaintext file format. The Ph.D. theses of students he has supervised are also online. Primary research interests center around numerical analysis, with an emphasis
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 Publications  J. F. Jardine; Mathematics Dept., Univ. of Western Ontario, Canada
On this page there are: a link to a full list of publications; a book subdirectory (Simplicial Homotopy Theory, by P. G. Goerss and J. F. Jardine); and abstracts of papers: A^1local symmetric spectra; Presheaves of symmetric spectra; A rigidity theorem
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 Public Understanding of Mathematics  Key Issues in Mathematics at the Math Forum
Links to organizations and articles that explore perceptions and assumptions nonmathematicians hold about mathematics and mathematicians.
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 Publishing and Journals  Dept. of Statistics, University of California at Los Angeles (UCLA)
Journals and book series edited by UCLA Statistics faculty, and/or distributed by UCLA Statistical Consulting. Journals: Evaluation Review; Journal of Educational and Behavioral Statistics; Journal of Multivariate Analysis; Journal of Statistical Software.
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 Pulchritudinous Primes
Visualizing the distribution of prime numbers: graphical investigations in 2D, 3D, Prime Island, The Ulam Spiral Phenomenon, Triangle Numbers on the Ulam Spiral. With an introduction, Why Primes?
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 Punctured Polyhedra  Ivars Peterson (MathTrek)
A tetrahedron has four triangular faces, four vertices, and six edges. When a vertex of one tetrahedron pierces the face of a second tetrahedron it forms a new, more complicated polyhedron: one triangular face has a triangular "hole" where the face was
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 Putnam Competition  Patrick J. Fitzsimmons
Postscript, Adobe Acrobat, and dvi downloads of problem sets from the William Lowell Putnam Mathematical Competition dating back to 1980. With links to solutions hosted by others, and information on participation.
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 PuzzleBeast  James W. Stephens
A collection of computergenerated puzzles, some illustrated with Java applets, some with solutions included: The Fried Okra Perplexity, A Dozen Irritating Sliding Block Puzzles, The Bulbous Blob Puzzle, Meandering Monk Maze, The Kung Fu Packing Crate
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 Puzzle Fun  Rodolfo Kurchan
An online newsletter edited by Rodolfo Kurchan (Buenos Aires  Argentina) about polyominoes and other puzzles. Back issues are on the Web.
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 Puzzle of the Week  Ralph Grove
A small archive of math and word puzzles having to do with patterns, permutations, and probability, with solutions, from a professor of computer science at Indiana University of Pennsylvania.
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 Puzzle Page  The Black Stump Ltd.
More than 150 links to puzzle sites on the Web. A new site is added each week.
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 Puzzles  Martin Watson
Blogs, comments, musings, design sketches, and photographs of mechanical puzzles by an avid collector and craftsman. Puzzle news, the author's own burrs (Watson's wormhole, digigrams, Dutch cubist), indepth explorations of manipulative puzzles (Puzzles
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Puzzles/Oneplayer Games  Jürg Nievergelt
Rubik's Cube and its variants. The 3*3*3* cube; Rubik's Revenge (4*4*4 cube); Pyramix (tetrahedron); Rubik's Clock; Rubik's Magic. Also Cryptequations, polyominoes, and links to a list of similar puzzles.
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 Puzzles, & Riddles  The Contest Center  Frank Rubin
Hundreds of puzzles and mathematical problems ranging from kindergarten through postdoctoral levels. For the easier puzzles, answers are provided on the site; names of those who submit correct solutions to harder problems are posted. See also Puzzles
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 The Puzzle TOAD  Tom Bohman, Oleg Pikhurko, Alan Frieze, and Danny Sleator, School of Computer Science, Carnegie Mellon University
Send the authors your solutions to their challenging graph theory, number theory, geometry, discrete mathematics, logic, and other puzzles. Revisit periodically to see the latest question, and download PDFs of solutions of past problems.
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 Puzzle Toons, The Citizen Scientist  Brian Mansfield
A comic strip devoted to puzzles, mind benders, and brain teasers. The subject matter of the puzzles ranges from mechanical devices and geometry to astrodynamics, chess, and billiards. Read back issues of Mansfield's column, dating to its inception in
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 Puzzle University  Amy Galitzer
A nonaccredited "university," created solely for fun. Everything is free to play and take part in. Register, pass a simple test, and advance from freshman to sophomore to junior to senior to grad student this way. The puzzles get harder as you progress.
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 Puzzle Workshop  maths online  University of Vienna, Austria
Make your own interactive "jigsaw," or multiple choice puzzles, to save and run on your own computer or to publish on the web. The Applet puzzle creation page requires Java; the Test puzzle creation page allows greater use of mathematical symbols.
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 Puzzle World  John Rausch
A searchable site with information and a discussion group (Puzzle Talk) about handcrafted mechanical puzzles. Most of the puzzles presented here are not the massproduced variety found in stores, but limited production puzzles produced by craftsmen (often
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 Puzzling Lines  Ivars Peterson (MathTrek)
Sol LeWitt has often featured geometric and combinatorial themes in his sculptures, paintings, and drawings. In 1973 he composed "Straight Lines in Four Directions and All Their Possible Combinations," a grid of 15 squares, each inscribed with one or
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 Puzzling Primes  Isaac Reed
To fully comprehend our number system, mathematicians need to understand the properties of the prime numbers  but even finding them isn't so easy.
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 The Puzzling World of Barry R. Clarke  Barry R. Clarke
Brain teasers from Clarke's column in The Daily Telegraph (UK) and from his various puzzle books: liar problems, logic teasers, number conundrums, matchstick puzzles, lateral mindbenders, and more. With links to other puzzles sites and an article on
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 pysimplex  Aaron Watters
Mixed Integer Linear programming modules: pysimplex provides some basic symbolic programming tools for constructing, solving and optimizing systems of linear equations and inequalities. It includes an implementation of the classical SIMPLEX linear optimization
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 Pythagoras Plays Ball  Ivars Peterson (MathLand)
Spring, baseball, statistics, math. In many ways, baseball is a numbers game: Strikeouts, home runs, batting averages, innings pitched, complete games, earned run averages, number of players left on base in scoring position in the bottom of the ninth
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 Pythagoras' Theorem: Elaboration on the Similarity Argument  Interactive Mathematics Miscellany and Puzzles, Alexander Bogomolny
Euclid included two proofs of the Pythagorean theorem in his Elements. A better known Proposition I.47 (Bride's chair) and VI.31 which is consistently overlooked in the introductory geometry courses. The latter,
however, renders the theorem virtually
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 Pythagoras' Theorem in Babylonian Mathematics  MacTutor Math History Archives
Linked essay examining four Babylonian tablets that all have some connection with the Pythagorean theorem. With references and other related web sites.
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 Pythagorean Puzzle (SMILE)  Earl Zwicker, Illinois Institute of Technology
A lesson that models the phenomenological approach to enable students to prove the Pythagorean Theorem on their own using puzzle pieces and working together.
From the Geometry and Measurement and Algebra and Trigonometry sections of a collection of almost
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 Pythagorean Theorem  Over 20 Proofs  Interactive Mathematics Miscellany and Puzzles, Alexander Bogomolny
A general exposition of the Pythagorean theorem, with proofs from Euclid to Garfield  and more. Also links to other sites on the Web with proofs.
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 Pythagorean Triples  H.B. Meyer
A Javascript calculator for pythagorean triples. In English and German.
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 Pythagoreisches Tripelprogramm  Heinz Becker
A Java applet that reads a and gives integer solutions of a^2+b^2 = c^2. In German and English.
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 Pythagoräische Tripel (Pythagorean Triplets)  H. B. Meyer
A calculator for Pythagorean triplets, making visible the oneto one correspondence between triplets and certain pairs of relatively prime numbers, and an interesting correspondence with certain sequences of letters A, B, or C. (Javascript is required.)
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 QAMA  QAMA, LLC
"The calculator that thinks only if you think, too," QAMA requires the operator to first enter a reasonable estimate. QAMA encourages rounding and rapid backoftheenvelope reckoning, but does not tolerate errors of magnitude or sign, or of basic operations
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