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Computing all monogeneous mixed dihedral quartic extensions of a quadratic field

István GaálGábor Nyul — 2001

Journal de théorie des nombres de Bordeaux

Let M be a given real quadratic field. We give a fast algorithm for determining all dihedral quartic fields K with mixed signature having power integral bases and containing M as a subfield. We also determine all generators of power integral bases in K . Our algorithm combines a recent result of Kable [9] with the algorithm of Gaál, Pethö and Pohst [6], [7]. To illustrate the method we performed computations for M = ( 2 ) , ( 3 ) , ( 5 ) .

Matchings in complete bipartite graphs and the r -Lah numbers

Gábor NyulGabriella Rácz — 2021

Czechoslovak Mathematical Journal

We give a graph theoretic interpretation of r -Lah numbers, namely, we show that the r -Lah number n k r counting the number of r -partitions of an ( n + r ) -element set into k + r ordered blocks is just equal to the number of matchings consisting of n - k edges in the complete bipartite graph with partite sets of cardinality n and n + 2 r - 1 ( 0 k n , r 1 ). We present five independent proofs including a direct, bijective one. Finally, we close our work with a similar result for r -Stirling numbers of the second kind.

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