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Forcing a $K_6$-minor ★★
Author(s): Barát ; Joret; Wood
-minor.
-minor. Keywords: connectivity; graph minors
Funcoidal products inside an inward reloid ★★
Author(s): Porton
then
for every funcoid
and atomic f.o.
and
on the source and destination of
correspondingly. A stronger conjecture:
then
for every funcoid
and
,
. Keywords: inward reloid
Odd cycles and low oddness ★★
Author(s):
the cycles of any
-factor are odd, then
, where
denotes the oddness of the graph
, that is, the minimum number of odd cycles in a
-factor of
. Keywords:
Odd perfect numbers ★★★
Author(s): Ancient/folklore
Keywords: perfect number
Matching cut and girth ★★
Author(s):
does there exists a
such that every graph with average degree smaller than
and girth at least
has a matching-cut? Keywords: matching cut, matching, cut
Strong 5-cycle double cover conjecture ★★★
Author(s): Arthur; Hoffmann-Ostenhof
be a circuit in a bridgeless cubic graph
. Then there is a five cycle double cover of
such that
is a subgraph of one of these five cycles. Keywords: cycle cover
Characterizing (aleph_0,aleph_1)-graphs ★★★
Call a graph an
-graph if it has a bipartition
so that every vertex in
has degree
and every vertex in
has degree
.
-graphs. Keywords: binary tree; infinite graph; normal spanning tree; set theory
The Berge-Fulkerson conjecture ★★★★
is a bridgeless cubic graph, then there exist 6 perfect matchings
of
with the property that every edge of
is contained in exactly two of
.
Keywords: cubic; perfect matching
Obstacle number of planar graphs ★
Author(s): Alpert; Koch; Laison
Does there exist a planar graph with obstacle number greater than 1? Is there some
such that every planar graph has obstacle number at most
?
Keywords: graph drawing; obstacle number; planar graph; visibility graph
Twin prime conjecture ★★★★
Author(s):
so that both
and
are prime.
Keywords: prime; twin prime
Cores of strongly regular graphs ★★★
Keywords: core; strongly regular
Square achievement game on an n x n grid ★★
Author(s): Erickson
grid. The first player (if any) to occupy four cells at the vertices of a square with horizontal and vertical sides is the winner. What is the outcome of the game given optimal play? Note: Roland Bacher and Shalom Eliahou proved that every 15 x 15 binary matrix contains four equal entries (all 0's or all 1's) at the vertices of a square with horizontal and vertical sides. So the game must result in a winner (the first player) when n=15. Keywords: game
What is the largest graph of positive curvature? ★
Keywords: curvature; planar graph
Extension complexity of (convex) polygons ★★
Author(s):
The extension complexity of a polytope
is the minimum number
for which there exists a polytope
with
facets and an affine mapping
with
.
, a convex polygon on
vertices whose extension complexity is
? Keywords: polytope, projection, extension complexity, convex polygon
Strict inequalities for products of filters ★
Author(s): Porton
for some filter objects
,
. Particularly, is this formula true for
? A weaker conjecture:
for some filter objects
,
. Keywords: filter products
Barnette's Conjecture ★★★
Author(s): Barnette
Keywords: bipartite; cubic; hamiltonian
Covering a square with unit squares ★★
Author(s):
, it is impossible to cover a square of side greater than
with
unit squares. Keywords:
Sequence defined on multisets ★★
Author(s): Erickson
array of positive integers where the first row consists of some distinct positive integers arranged in increasing order, and the second row consists of any positive integers in any order. Create a new array where the first row consists of all the integers that occur in the first array, arranged in increasing order, and the second row consists of their multiplicities. Repeat the process. For example, starting with the array
, the sequence is:
->
->
->
->
->
->
->
->
->
->
->
, and we now have a fixed point (loop of one array).
The process always results in a loop of 1, 2, or 3 arrays.
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