Research problems (Q5970608)

Problem 243, Positive power series, posed by François Bergeron. Problem 244, Generalizations of the Greene-Kleitman theorem, posed by Sergey Fomin. Problem 245, An extremal problem, posed by Laurent Habsieger. Problem 246, A generalized Cauchy identity, posed by David M. Jackson. Problem 247, An identity for maps on orientable surfaces, posed by David M. Jackson. Problem 248, An identity for permutations, posed by David M. Jackson. Problem 249, Combinatorial algorithms concerning the class-algebra of the symmetric group, posed by Jacob Katriel. Problem 250, Correlations in random domino tilings, posed by Jim Propp. Problem 251, Spanning trees of Aztec diamonds, posed by Richard P. Stanley. Problem 252, Classifying Ehrhart polynomials of lattice simplices, posed by Einar Steingrímsson. Problem 253, A recognition problem for a class of partially ordered sets, posed by David Wagner.