let tables = list $
    each sheet-names name ↦
        wb ⊳ sheet name ⊳ table

let pubs =
    each tables table ↦
        table ⊳ column "Publisher"
    ⊳ chain
    ⊳ unique
    ⊳ list

let pub-tables =
    each pubs pub ↦
        tuple pub $
            zip sheet-names tables
            ⊳ each [sheet-name table] ↦
                tuple sheet-name $
                    table ⊳ filter (row ↦ (row "Publisher") = pub)