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EJC
2010
13 years 10 months ago
2010
This article presents new bijections on planar maps. At first a bijection is established between bipolar orientations on planar maps and specific "transversal structures"...
EJC
2010
13 years 10 months ago
2010
In a recent paper, Amini et al. introduced a general framework to prove duality theorems between tree decompositions and their dual combinatorial object. They unify all known ad-h...
EJC
2010
13 years 10 months ago
2010
A classical result of Euler states that the tangent numbers are an alternating sum of Eulerian numbers. A dual result of Roselle states that the secant numbers can be obtained by a...
EJC
2010
13 years 10 months ago
2010
A Shilla distance-regular graph (say with valency k) is a distance-regular graph with diameter 3 such that its second largest eigenvalue equals to a3. We will show that a3 divide...
EJC
2010
13 years 10 months ago
2010
Each clone C on a fixed base set A determines a quasiorder on the set of all operations on A by the following rule: f is a C-minor of g if f can be obtained by substituting operati...