BCFG classification of symmetric Lagrangian fillings

Let Λ(β)(S3,ξst)\Lambda(\beta)\subseteq(\mathbb{S}^3,\xi_{\mathrm{st}}) be the Legendrian rainbow closure of a positive braid β\beta. An exact Lagrangian GG-filling is an exact Lagrangian filling invariant under a faithful finite-group action GG by exact symplectomorphisms, with G(Λ)=ΛG(\Lambda)=\Lambda setwise.

BCFG classification of Lagrangian fillings. The following symmetric cases have the stated numbers of fillings:

  1. If Λ(β)=Λ(A2n1)\Lambda(\beta)=\Lambda(A_{2n-1}), the indicated Z2\mathbb{Z}_2-symmetry lifts to a Z2\mathbb{Z}_2-symmetry of Λ(A2n1)\Lambda(A_{2n-1}), which has precisely (2nn)\binom{2n}{n} exact Lagrangian Z2\mathbb{Z}_2-fillings.
  2. If Λ(β)=Λ(Dn+1)\Lambda(\beta)=\Lambda(D_{n+1}), the indicated Z2\mathbb{Z}_2-symmetry lifts to a Z2\mathbb{Z}_2-symmetry of Λ(Dn+1)\Lambda(D_{n+1}), which has precisely (2nn)\binom{2n}{n} exact Lagrangian Z2\mathbb{Z}_2-fillings.
  3. If Λ(β)=Λ(E6)\Lambda(\beta)=\Lambda(E_6), the indicated Z2\mathbb{Z}_2-symmetry lifts to a Z2\mathbb{Z}_2-symmetry of Λ(E6)\Lambda(E_6), which has precisely 105105 exact Lagrangian Z2\mathbb{Z}_2-fillings.
  4. If Λ(β)=Λ(D4)\Lambda(\beta)=\Lambda(D_4), the indicated Z3\mathbb{Z}_3-symmetry lifts to a Z3\mathbb{Z}_3-symmetry of Λ(D4)\Lambda(D_4), which has precisely 88 exact Lagrangian Z3\mathbb{Z}_3-fillings.

This extends the ADE perspective to the folded types BnB_n, CnC_n, F4F_4, and G2G_2, where the additional symmetry is part of the classification. The statement is presented as plausible rather than established, so the status of these enumerations remains open.

Sources & referencesView supporting material

Primary source

Roger Casals, “Lagrangian Skeleta and Plane Curve Singularities”, arXiv:2009.06737 (2020).

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