Tag Archives: Dima Fon-Der-Flaass

Bijective proofs

A fourth proof Last month I described three proofs of the formula for the number of ways to choose k objects from a set of n, if repetition is allowed and order is not significant; it is the same as … Continue reading

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The definition of a matroid

This post continues my series about definitions. It has been obvious from the earliest days of the subject that matroids can be defined in very many different ways: in terms of their independent sets, their bases (maximal independent sets), their … Continue reading

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