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Randomness plays an integral role in modern combinatorics,
particularly when constructions are desired. However, it is often
unsatisfying to call a randomly selected object a construction, as no
explicit description is given. This problem is notorious throughout
Ramsey theory, number theory, and elsewhere. Since probabilistic methods
have been so successful, it would be desirable to provide constructions
that resemble random ones in salient ways, and, furthermore, to be able
to measure the randomness of an object or class of objects. In fact,
such measures have important applications in structural combinatorics.
Quasirandomness is one such perspective on quantifying randomness. The
set of properties true with high probability in a combinatorial space
are partially ordered by implication; cliques of mutually equivalent
properties may be identified and given the induced ordering.
Surprisingly large sets of natural random-like properties have been
shown to belong to a single one of these property cliques in the case of
graphs, hypergraphs, tournaments, and subsets of the finite cyclic groups.
In this talk, we discuss quasirandom permutations, a subject that
relates discrepancy theory, permutation statistics, discrete harmonic
analysis, and numerical integration. Almost all natural number-theoretic
permutations turn out to be highly quasirandom, and determining the
relevant bounds provides a wealth of interesting questions in the theory
of exponential sums. We discuss these and other examples, including the
class of optimally quasirandom permutations, and we present several
intriguing questions in this realm.
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