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        "datetime_start":"20260410T143000",
        "datetime_end":"20260410T153000",
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        "date_start":"2026-04-10",
        "date_end":"2026-04-10",
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        "event_title":"Representation stability via Young symmetrizers and a new ribbon basis for the rank-selected homology of the partition lattice (Combinatorics seminar)",
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        "combined_title":"Representation stability via Young symmetrizers and a new ribbon basis for the rank-selected homology of the partition lattice (Combinatorics seminar): Patricia Hersh (University of Oregon)",
        "event_subtitle":"Patricia Hersh (University of Oregon)",
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        "description":"In this talk, we will begin with a quick review of group actions on posets, rank-selected homology of posets, representation stability, and a nice way of interpreting the rank-selected homology of the Boolean lattice as a Specht module of ribbon shape.  This interpretation allows us to prove a sharp representation stability bound for the rank-selected homology of the Boolean lattice.  We then describe a new \u200bribbon basis for the rank-selected homology of any geometric lattice.  In the case of the partition lattice, this ribbon basis interacts with Young symmetrizers in much the way a traditional Specht module would.   Using this basis, we prove a sharp representation stability bound for the rank-selected homology of the partititon lattice, a bound that had  previously been conjectured by the speaker and Vic Reiner.   This is joint work with Sheila Sundaram.",
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    {
        "datetime_modified":"20260331T111638",
        "datetime_start":"20260417T143000",
        "datetime_end":"20260417T153000",
        "has_end_time":1,
        "date_start":"2026-04-17",
        "date_end":"2026-04-17",
        "time_start":"14:30:00",
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        "time_zone":"America\/Detroit",
        "event_title":"A positive combinatorial formula for the double Edelman\u2013Greene coefficients (Combinatorics seminar)",
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        "combined_title":"A positive combinatorial formula for the double Edelman\u2013Greene coefficients (Combinatorics seminar): Tianyi Yu (UQAM)",
        "event_subtitle":"Tianyi Yu (UQAM)",
        "event_type":"Workshop \/ Seminar",
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        "description":"Lam, Lee, and Shimozono introduced the double Stanley symmetric functions in their study of the equivariant geometry of the affine Grassmannian. They proved that the associated double Edelman\u2013 Greene coefficients, the double Schur expansion of these functions, are positive, a result later refined by Anderson. They further asked for a combinatorial proof of this positivity. We provide the first such proof, together with a combinatorial formula that manifests the finer positivity established by Anderson. Our formula is built from two combinatorial models: bumpless pipedreams and increasing chains in the Bruhat order. The proof relies on three key ingredients: a correspondence between these two models, a natural subdivision of bumpless pipedreams, and a symmetry property of increasing chains. This talk is based on joint work with Jack Chou.",
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        "datetime_start":"20260508T143000",
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        "date_start":"2026-05-08",
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        "time_zone":"America\/Detroit",
        "event_title":"Combinatorics seminar -- TBA",
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        "combined_title":"Combinatorics seminar -- TBA: Alexander Guterman (Bar-Ilan University)",
        "event_subtitle":"Alexander Guterman (Bar-Ilan University)",
        "event_type":"Workshop \/ Seminar",
        "event_type_id":"21",
        "description":"TBA",
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        "location_name":"East Hall",
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