@Article{         Langford:AM:1926,
  Author        = "Langford, C. H.",
  date-added    = "2017-11-02 10:15:17 +0000",
  date-modified = "2020-05-21 14:58:07 +0200",
  ISSN          = "0003486X",
  Journal       = "Annals of Mathematics",
  Number        = "1/4",
  Pages         = "16--40",
  Publisher     = "Annals of Mathematics",
  Title         = "Some Theorems on Deducibility",
  URL           = "http://www.jstor.org/stable/1968352",
  Volume        = "28",
  Year          = "1926",
  bdsk-url-1    = "http://www.jstor.org/stable/1968352",
  File          = "Some Theorems on Deducibility - langford1926 - a - l.pdf"
}

@Article{ Langford:AM:1926, Author = "Langford, C. H.", date-added = "2017-11-02 10:15:17 +0000", date-modified = "2020-05-21 14:58:07 +0200", ISSN = "0003486X", Journal = "Annals of Mathematics", Number = "1/4", Pages = "16--40", Publisher = "Annals of Mathematics", Title = "Some Theorems on Deducibility", URL = "http://www.jstor.org/stable/1968352", Volume = "28", Year = "1926", bdsk-url-1 = "http://www.jstor.org/stable/1968352", File = "Some Theorems on Deducibility - langford1926 - a - l.pdf" }