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Slicing cones in various ways with a plane generates conic sections identified geometrically as hyperbolas, parabolas, or ellipses and algebraically, when suitably rotated, as certain rescaled quadratic polynomials, or forms, in two variables.

The refined face partition polynomials of the permutohedra (OEIS A049019) and associahedra (or Stasheff polytopes, A133437) and partition polynomials for noncrossing partitions (A134264) can all be algebraically related by re-scaling the associated monomials per the calculus of compositional and multiplicative inversion of power series, so this represents the algebraic analogue of the rescaling of the quadratic equations for conics.

Which geometric structures, such as possibly the noncrossing hypertrees of McCammond, brick polytopes, or simply polygons, when "sliced" in different ways, provide  representations of permutohedra, associahedra, and noncrossing partitions?

Ancillary question: Is there a geometric complex (possibly the Whitehouse simplicial complex, related to phylogenetic trees, or the trees themselves) that can be associated to Lagrange (compositional) inversion of exponential generating functions (i.e., formal Taylor, or divided powers, series) and can be incorporated in this geometric scheme if one exists?

Tom Copeland
  • 9,937
  • Related: https://oeis.org/A102537; Einziger, (http://pqdtopen.proquest.com/doc/750317016.html?FMT=ABS) Incidence Hopf algebras: Antipodes, forest formulas, and noncrossing partitions; J. McCammond, (http://web.math.ucsb.edu/~jon.mccammond/papers/index.html) Noncrossing Hypertrees; J.-C. Novelli, J.-Y. Thibon, (http://arxiv.org/abs/1403.5962) Hopf Algebras of m-permutations,(m+1)-ary trees, and m-parking functions; E. Tzanaki, (http://arXiv.org/abs/math.CO/0501100) Polygon dissections and some generalizations of cluster complexes. – Tom Copeland May 19 '17 at 21:13
  • Related to ancillary Q: https://oeis.org/A134991 – Tom Copeland May 19 '17 at 22:13
  • See "Hopf monoids and generalized permutohedra" by Aguiar and Ardila https://arxiv.org/abs/1709.07504 – Tom Copeland Dec 01 '17 at 18:40
  • Related "Relating the associahedron and the permutohedron" by Tonks https://pdfs.semanticscholar.org/80c9/c4cef0a9c7cec3de650e6d8fb7ca9f5f966b.pdf – Tom Copeland Dec 11 '19 at 01:08
  • Cf. "Hopf Algebra of the Planar Binary Trees" by Loday and Ronco. – Tom Copeland Apr 04 '20 at 16:11

1 Answers1

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2-truncated cubes provide the "slicings" to generate the associahedra or permutahedra.

See "Upper and lower bound theorems for graph-associahedra" by Buchstaber and Volodin, "Cubical realizations of flag nestohedra and Gal's conjecture" by Volodin, and "Geometric realization of $\gamma$-vectors of 2-truncated cubes" by Volodin.

There is a video of a cube being truncated to form a 3-D permutahedron (truncated octahedron) at a website maintained by Vera Viana.

Tom Copeland
  • 9,937
  • And "The diagonal of the associahedra" by Naruki Masuda, Hugh Thomas, Andy Tonks, Bruno Vallette https://arxiv.org/abs/1902.08059 – Tom Copeland Sep 07 '19 at 13:41
  • See also "Diagonals on the Permutahedra, Multiplihedra and Associahedra" by Samson Saneblidze, Ronald Umble https://arxiv.org/abs/math/0209109 – Tom Copeland Sep 07 '19 at 17:03
  • "Direct families of polytopes with nontrivial Massey products" by Victor Buchstaber and Ivan Limonchenko https://arxiv.org/abs/1811.02221 – Tom Copeland Mar 21 '20 at 18:08
  • See also p. 16 of "Toric Topology of Stasheff Polytopes" by Buchstaber – Tom Copeland Sep 30 '20 at 20:44
  • See Fig. 1.4 on p. 18 of "From permutahedra to associahedra, a walk through geometric and algebraic combinatorics" by Vincent Pilaud http://www.lix.polytechnique.fr/~pilaud/documents/reports/habilitationVincentPilaud.pdf – Tom Copeland Oct 25 '20 at 20:24
  • From "Convex Polytopes and Enumeration" by Rodica Simion: "... the permutohedron, the associahedron, polytopes arising as intersections of cubes and simplices with half-spaces ... ." – Tom Copeland Nov 11 '20 at 21:21
  • See also "Combinatorial 2-truncated Cubes and Applications" by Buchstaber and Volodin in the book Associahedra, Tamari Lattices and Related Structures: Tamari Memorial Festschrift (editors: Müller-Hoissen, Pallo, Stasheff). – Tom Copeland May 28 '21 at 15:52