Equality of the sorting classes for the 312-type stack-sorting maps

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Let SC312\text{SC}_{312}, SC31‾2\text{SC}_{\underline{31}2}, and SC312‾\text{SC}_{3\underline{12}} be the vincular-pattern-avoiding stack-sorting maps, and let Sortn(f)\text{Sort}_n(f) denote the permutations in Sn\mathfrak S_n mapped to the identity by s∘fs\circ f. Equality conjecture. The sorting classes of SC31‾2\text{SC}_{\underline{31}2} and SC312‾\text{SC}_{3\underline{12}} are identical:

Sortn(SC312)=Sortn(SC31‾2)=Sortn(SC312‾).\text{Sort}_n(\text{SC}_{312})=\text{Sort}_n(\text{SC}_{\underline{31}2})=\text{Sort}_n(\text{SC}_{3\underline{12}}).

Furthermore, for every τ∈Sortn(SC312)\tau\in\text{Sort}_n(\text{SC}_{312}),

SC312(τ)=SC31‾2(τ)=SC312‾(τ).\text{SC}_{312}(\tau)=\text{SC}_{\underline{31}2}(\tau)=\text{SC}_{3\underline{12}}(\tau).

The maps SC31‾2\text{SC}_{\underline{31}2} and SC312‾\text{SC}_{3\underline{12}} are being compared because their sorting-class cardinalities agree in the computed cases and the corresponding classical and vincular maps coincide in related free-stack situations. The equality of the classes and of their values on the sorting class remains conjectural.

References

Primary source

William Zhao, “Stack-sorting with Stacks Avoiding Vincular Patterns”, arXiv:2410.17057 (2024).

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