BCFG classification of symmetric Lagrangian fillings

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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(A2n−1)\Lambda(\beta)=\Lambda(A_{2n-1}), the indicated Z2\mathbb{Z}_2-symmetry lifts to a Z2\mathbb{Z}_2-symmetry of Λ(A2n−1)\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.

References

Primary source

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

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