arminstraub.com

The "What Is...?" column

I very much enjoy reading the "What Is...?" column in the Notices of the AMS. Unfortunately, there seemed to be no index to this column. I have therefore created this one in the hope that it might be helpful to others as well.

(A few years later, there now exists the following overview of the What Is Collection.)

  1. What is... the Dirac equation? — M. Burak Erdoğan, William R. Green, and Ebru Toprak, November 2021
  2. What is... a companion? — Anna Cadoret, August 2021
  3. What is... the VC-Dimension? — Samuel C. Tenka, April 2021
  4. What is... a hyperpolygon? — Steven Rayan and Laura P. Schaposnik, January 2021
  5. What is... a minuscule representation? — Richard M. Green, June/July 2020
  6. What is... a hereditarily indecomposable Banach space? — Hossein Hosseini Giv, October 2019
  7. What is... a Markov basis? — Sonja Petrović, August 2019
  8. What is... a thin group? — Alex Kontorovich, D. Darren Long, Alexander Lubotzky, and Alan W. Reid, June/July 2019
  9. What is... a Coleman integral? — Jennifer S. Balakrishnan, May 2019
  10. What is... Falconer's conjecture? — Alex Iosevich, April 2019
  11. What is... a multilayer network? — Mason A. Porter, December 2018
  12. What is... a Borel reduction? — Matthew Foreman, November 2018
  13. What is... a rectifiable set? — Editors, October 2018
  14. What is... a matroidal family of graphs? — J. M. S. Simões-Pereira, September 2018
  15. What is... Riemannian holonomy? — Jacob Gross, August 2018
  16. What is...the Langlands Program? — Solomon Friedberg, June/July 2018
  17. What is...a hyperbolic 3-manifold? — Colin Adams, May 2018
  18. What is... hypoellipticity? — Editors, April 2018
  19. What is...an information projection? — Frank Nielsen, March 2018
  20. What is...the amplituhedron? — Jacob Bourjaily and Hugh Thomas, February 2018
  21. What is...an acylindrical group action? — Thomas Koberda, January 2018
  22. What is...a scheme? — Tom Gannon, December 2017
  23. What is...a varifold? — Editors, November 2017
  24. What is... perimeter? — Editors, October 2017
  25. What is...a Sobolev orthogonal polynomial? — Francisco Marcellán and Juan J. Moreno-Balcázar, September 2017
  26. What is...a CR submanifold? — Phillip S. Harrington and Andrew Raich, August 2017
  27. What is...a generalised mean-curvature flow? — Hui Yu, June/July 2017
  28. What is...a virtual knot? — Daniel S. Silver, Susan G. Williams, May 2017
  29. What is... tropical geometry? — Eric Katz, April 2017
  30. What is... an elliptic curve? — Harris B. Daniels and Álvaro Lozano-Robledo, March 2017
  31. What is... Benford's Law? — Arno Berger, Theodore P. Hill, February 2017
  32. What is...a complex symmetric operator? — Stephan Ramon Garcia, January 2017
  33. What is... symplectic geometry? — Tara S. Holm, December 2016
  34. What is...a blender? — Ch. Bonatti, S. Crovisier, L. J. Díaz, A. Wilkinson, November 2016
  35. What is...a multiple orthogonal polynomial? — Andrei Martínez-Finkelshtein and Walter Van Assche, October 2016
  36. What is...a Leavitt path algebra? — Gene Abrams, September 2016
  37. What is...a Diophantine m-tuple? — Andrej Dujella, August 2016
  38. What is... aperiodic order? — Michael Baake, David Damanik and Uwe Grimm, June/July 2016
  39. What is... Nash equilibrium? — Rajiv Sethi and Jörgen Weibull, May 2016
  40. What is...a quandle? — Sam Nelson, April 2016
  41. What is...an anabelian scheme? — Kirsten Wickelgren, March 2016
  42. What is... Gauss curvature? — Editors, February 2016
  43. What is...an ergodic transformation? — Cesar E. Silva, January 2016
  44. What is...an automatic sequence? — Eric Rowland, March 2015
  45. What is...a graphon? — Daniel Glasscock, January 2015
  46. What is...a perfectoid space? — Bhargav Bhatt, October 2014
  47. What is...a period? — Stefan Müller-Stach, September 2014
  48. What is...a Rauzy fractal? — Pierre Arnoux, Edmund Harriss, August 2014
  49. What is...a spectrahedron? — Cynthia Vinzant, May 2014
  50. What is... cyclic sieving? — Victor Reiner, Dennis Stanton, Dennis White, February 2014
  51. What is...a flag algebra? — Alexander A. Razborov, November 2013
  52. What is...the Leech lattice? — Chuanming Zong, October 2013
  53. What is...the p-adic Mandelbrot set? — Joseph H. Silverman, September 2013
  54. What is...a frame? — Christopher Heil, June/July 2013
  55. What is...a tensegrity? — Robert Connelly, January 2013
  56. What is...a Shimura variety? — James S. Milne, December 2012
  57. What is... essential dimension? — Zinovy Reichstein, November 2012
  58. What is...a scissors congruence? — Johan L. Dupont, October 2012
  59. What is... cop number? — Anthony Bonato, September 2012
  60. What is...an octopus decomposition? — Larry Conlon, August 2012
  61. What is...a biholomorphic mapping? — Eric Bedford, June/July 2012
  62. What is...an approximate group? — Ben Green, May 2012
  63. What is... data mining? — Mauro Maggioni, April 2012
  64. What is...an affine sphere? — Daniel J. F. Fox, March 2012
  65. What is...a pseudoconvex domain? — R. Michael Range, February 2012
  66. What is...a Fenchel conjugate? — Heinz H. Bauschke, Yves Lucet, January 2012
  67. What is...a natural proof? — Timothy Y. Chow, December 2011
  68. What is...a stationary measure? — Alex Furman, October 2011
  69. What is... Thompson's group? — J. W. Cannon, W. J. Floyd, September 2011
  70. What is...a derived stack? — Gabriele Vezzosi, August 2011
  71. What is...a resplendent structure? — Roman Kossak, June/July 2011
  72. What is...a infra-nilmanifold endomorphism?? — Karel Dekimpe, May 2011
  73. What is...a G2-manifold? — Spiro Karigiannis, April 2011
  74. What is... equivariant cohomology? — Loring W. Tu, March 2011
  75. What is...a free cumulant? — Jonathan Novak, Piotr Sniady, February 2011
  76. What is... persistent homology? — Shmuel Weinberger, January 2011
  77. What is...a mock modular form? — Amanda Folsom, December 2010
  78. What is... cost? — Damien Gaboriau, November 2010
  79. What is...a linear algebraic group? — Skip Garibaldi, October 2010
  80. What is...a sandpile? — Lionel Levine, James Propp, September 2010
  81. What is...a paraproduct? — Árpád Bényi, Diego Maldonado, Virginia Naibo, August 2010
  82. What is...a kinetic solution for degenerate parabolic-hyperbolic equations? — Gui-Qiang G. Chen, Benoît Perthame, June/July 2010
  83. What is...a perverse sheaf? — Mark Andrea de Cataldo, Luca Migliorini, May 2010
  84. What is...a Wilf-Zeilberger pair? — Akalu Tefera, April 2010
  85. What is...a Gaussian entire function? — Fedor Nazarov, Mikhail Sodin, March 2010
  86. What is...a halting probability? — Cristian S. Calude, G. J. Chaitin, February 2010
  87. What is...an Oka manifold? — Finnur Larusson, January 2010
  88. What is...a Rota-Baxter algebra? — Li Guo, December 2009
  89. What is...a Legendrian knot? — Joshua M. Sabloff, November 2009
  90. What is...Stanley depth? — M. R. Pournaki, S. A. Seyed Fakhari, M. Tousi, S. Yassemi, October 2009
  91. What is...the complex dual to the real sphere? — Simon Gindikin, September 2009
  92. What is...the parity phenomenon? — John Friedlander, Henryk Iwaniec, August 2009
  93. What is...an elliptic genus? — Serge Ochanine, June/July 2009
  94. What is...measure rigidity? — Manfred Einsiedler, May 2009
  95. What is...Lehmer's number? — Eriko Hironaka, March 2009
  96. What is...a skein module? — W. B. Raymond Lickorish, February 2009
  97. What is...the Schwarzian derivative? — Valentin Ovsienko, Sergei Tabachnikov, January 2009
  98. What is...a period domain? — James Carlson, Phillip Griffiths, December 2008
  99. What is...a cross ratio? — François Labourie, November 2008
  100. What is...stable commutator length? — Danny Calegari, October 2008
  101. What is...an ∞-category? — Jacob Lurie, September 2008
  102. What is...outer space? — Karen Vogtmann, August 2008
  103. What is...forcing? — Thomas Jech, June/July 2008
  104. What is...a toric variety? — Ezra Miller, May 2008
  105. What is...property A? — Piotr Nowak, Guoliang Yu, April 2008
  106. What is...a systole? — Marcel Berger, March 2008
  107. What is...JPEG? — David Austin, February 2008
  108. What is...quantum chaos? — Ze'ev Rudnick, January 2008
  109. What is...a cluster algebra? — Andrei Zelevinsky, December 2007
  110. What is...Boy's surface? — Robion Kirby, November 2007
  111. What is...a Woodin cardinal? — John Steel, October 2007
  112. What is...a Higgs bundle? — Steve Bradlow, Oscar García-Prada, Peter Gothen, September 2007
  113. What is...a Galois representation? — Mark Kisin, June/July 2007
  114. What is...an infinite swindle? — Valentin Poénaru, May 2007
  115. What is...a tropical curve? — Grigory Mikhalkin, April 2007
  116. What is...a minimal model? — János Kollár, March 2007
  117. What is...a Young tableau? — Alexander Yong, February 2007
  118. What is...a projective structure? — William Goldman, January 2007
  119. What is...a quasiconformal mapping? — Juha Heinonen, December 2006
  120. What is...Turing reducibility? — Martin Davis, November 2006
  121. What is...a bad end? — Charles Epstein, October 2006
  122. What is...a quasicrystal? — Marjorie Senechal, September 2006
  123. What is...a strange attractor? — David Ruelle, August 2006
  124. What is...a coarse space? — John Roe, June/July 2006
  125. What is...percolation? — Harry Kesten, May 2006
  126. What is...a syzygy? — Roger Wiegand, April 2006
  127. What is...a graph minor? — Bojan Mohar, March 2006
  128. What is...a quantum group? — Shahn Majid, January 2006
  129. What is...a random matrix? — Persi Diaconis, December 2005
  130. What is...a Gröbner basis? — Bernd Sturmfels, November 2005
  131. What is...a pseudoholomorphic curve? — Simon Donaldson, October 2005
  132. What is...a Lefschetz pencil? — Robert Gompf, September 2005
  133. What is...a compacton? — Philip Rosenau, August 2005
  134. What is...property tau? — Alex Lubotzky, June/July 2005
  135. What is...a horseshoe? — Mike Shub, May 2005
  136. What is...a dimer? — Richard Kenyon, Andrei Okounkov, March 2005
  137. What is...a brane? — Gregory Moore, February 2005
  138. What is...an open book? — Emmanuel Giroux, January 2005
  139. What is...a flip? — Alessio Corti, December 2004
  140. What is...a motive? — Barry Mazur, November 2004
  141. What is...a topos? — Luc Illusie, October 2004
  142. What is...a grope? — Peter Teichner, September 2004
  143. What is...an expander? — Peter Sarnak, August 2004
  144. What is...an operad? — James Stasheff, June/July 2004
  145. What is...a free lunch? — Fredy Delbaen, Walter Schachermayer, May 2004
  146. What is...a billiard? — Yakov Sinai, April 2004
  147. What is...a quasi-morphism? — D. Kotschick, February 2004
  148. What is...a curvelet? — Emmanuel Candès, December 2003
  149. What is...a dessin d'enfant? — Leonardo Zapponi, August 2003
  150. What is...a bubble tree? — Thomas Parker, June/July 2003
  151. What is...a worm? — Harold Boas, May 2003
  152. What is...a stack? — Dan Edidin, April 2003
  153. What is...a train track? — Lee Mosher, March 2003
  154. What is...a gerbe? — Nigel Hitchin, February 2003
  155. What is...a shtuka? — David Goss, January 2003
  156. What is...an alteration? — Frans Oort, December 2002
  157. What is...a building? — Kenneth S. Brown, November 2002
  158. What is...the monster? — Richard Borcherds, October 2002
  159. What is...an amoeba? — Oleg Viro, September 2002