Differential equations for the exponential generating functions of two vincular avoidance classes

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Let [Π][\Pi] be a set of possibly vincular patterns, and define its exponential generating function by

E[Π]=∑n≥0#Av⁡n[Π]xnn!.E[\Pi]=\sum_{n\ge 0} \#\operatorname{Av}_n[\Pi]\frac{x^n}{n!}.

Write 123‾\overline{123} and 213‾\overline{213} for the two vincular patterns in question, and let E′=dEdxE'=\frac{dE}{dx}.

Conjectures. For E=E[123‾]E=E[\overline{123}] and for E=E[213‾]E=E[\overline{213}], respectively,

E′=E2−E+1,E'=E^2-E+1,

and

E′=eE−x22.E'=e^{E-\frac{x^2}{2}}.

These differential equations would determine the corresponding avoidance-class enumerations, since their explicit solutions can be found by separation of variables once the equations are proved. The source provides no resolution of either conjecture.

References

Primary source

Rachel Domagalski, Jinting Liang, Quinn Minnich, Bruce E. Sagan, Jamie Schmidt and Alexander Sietsema, “Cyclic Pattern Containment and Avoidance”, arXiv:2106.02534 (2021).

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