The strict ordering of non-one-block patterns

Let Πk\Pi_k be the set of partitions of [k][k], let βkΠk\beta_k\in\Pi_k be the partition with one block, and let Πn(τ)\Pi_n(\tau) denote the set of partitions of [n][n] avoiding τ\tau. Define τπ\tau\prec\pi when Πn(τ)Πn(π)|\Pi_n(\tau)|\leq |\Pi_n(\pi)| for all n>kn>k, with strict inequality for all sufficiently large nn.

Strict ordering conjecture. If k4k\geq 4, τΠk\tau\in\Pi_k, and τβk\tau\neq\beta_k, then

τβk\tau\prec\beta_k

and

Πn(τ)<Πn(βk)|\Pi_n(\tau)|<|\Pi_n(\beta_k)|

for all n>kn>k.

Computer evidence suggests this ordering, while the paper proves it for patterns with exactly two blocks; the assertion for all other patterns remains conjectural in the supplied text.

Sources & referencesView supporting material

Primary source

Jonathan Bloom and Dan Saracino, “Pattern avoidance for set partitions à la Klazar”, arXiv:1511.00192 (2016).

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