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

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

E[Π]=n0#Avn[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=E2E+1,E'=E^2-E+1,

and

E=eEx22.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.

Sources & referencesView supporting material

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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