Monthly Archives: August 2013

Equalizers of free monoid morphisms, supports of rational power series and a question of Pin

In this mathoverflow question, J.-E. Pin asked if it is decidable whether the support of a -rational power series in non-commuting variables is a regular language. I pointed out that the answer is no and will elaborate here because it … Continue reading

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Isomorphism of oriented matroids from a semigroup viewpoint

This is in some sense a sequel to this post. Basically, I want to show that the somewhat awkward, in my opinion, definition of isomorphism of oriented matroids found, for example, here can be interpreted as isomorphism of underlying unary … Continue reading

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