1,082 research outputs found
Symmetric colorings of polypolyhedra
Polypolyhedra (after R. Lang) are compounds of edge-transitive 1-skeleta.
There are 54 topologically different polypolyhedra, and each has
icosidodecahedral, cuboctahedral, or tetrahedral symmetry, all are realizable
as modular origami models with one module per skeleton edge. Consider a
coloring in which each edge of a given component receives a different color,
and where the coloring (up to global color permutation) is invariant under the
polypolyhedron's symmetry group. On the Five Intersecting Tetrahedra, the edges
of each color form visual bands on the model, and correspond to matchings on
the dodecahedron graph. We count the number of such colorings and give three
proofs. For each of the non-polygon-component polypolyhedra, there is a
corresponding matching coloring, and we count the number of these matching
colorings. For some of the non-polygon-component polypolyhedra, there is a
corresponding visual-band coloring, and we count the number of these band
colorings
Boolean algebras and Lubell functions
Let denote the power set of . A collection
\B\subset 2^{[n]} forms a -dimensional {\em Boolean algebra} if there
exist pairwise disjoint sets , all non-empty
with perhaps the exception of , so that \B={X_0\cup \bigcup_{i\in I}
X_i\colon I\subseteq [d]}. Let be the maximum cardinality of a family
\F\subset 2^X that does not contain a -dimensional Boolean algebra.
Gunderson, R\"odl, and Sidorenko proved that where .
In this paper, we use the Lubell function as a new measurement for large
families instead of cardinality. The Lubell value of a family of sets \F with
\F\subseteq \tsupn is defined by h_n(\F):=\sum_{F\in \F}1/{{n\choose |F|}}.
We prove the following Tur\'an type theorem. If \F\subseteq 2^{[n]} contains
no -dimensional Boolean algebra, then h_n(\F)\leq 2(n+1)^{1-2^{1-d}} for
sufficiently large . This results implies , where is an absolute constant independent of and . As a
consequence, we improve several Ramsey-type bounds on Boolean algebras. We also
prove a canonical Ramsey theorem for Boolean algebras.Comment: 10 page
Rainbow Ramsey problems for the Boolean lattice
We address the following rainbow Ramsey problem: For posets what is the
smallest number such that any coloring of the elements of the Boolean
lattice either admits a monochromatic copy of or a rainbow copy of
. We consider both weak and strong (non-induced and induced) versions of
this problem. We also investigate related problems on (partial) -colorings
of that do not admit rainbow antichains of size
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