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@Book{            BuchiSiefkes,
  Author        = {B{\"u}chi, Richard and Siefkes, Dirk},
  date-added    = "2020-04-10 11:07:26 +0200",
  date-modified = "2020-04-10 11:07:26 +0200",
  Publisher     = "Springer-Verlag",
  Title         = "Decidable Theories II - The Monadic Second Order Theory of All Countable Ordinals",
  Year          = "1973",
  File          = "Decidable Theories II - The Monadic Second Order Theory of All Countable Ordinals - Büchi, Siefkes (0) (0) - a - a.pdf"
}

@Book{ BuchiSiefkes, Author = {B{\"u}chi, Richard and Siefkes, Dirk}, date-added = "2020-04-10 11:07:26 +0200", date-modified = "2020-04-10 11:07:26 +0200", Publisher = "Springer-Verlag", Title = "Decidable Theories II - The Monadic Second Order Theory of All Countable Ordinals", Year = "1973", File = "Decidable Theories II - The Monadic Second Order Theory of All Countable Ordinals - Büchi, Siefkes (0) (0) - a - a.pdf" }