@Article{         Gentzen:1934,
  Author        = "Gentzen, Gerhard",
  date-added    = "2020-09-08 09:42:50 +0200",
  date-modified = "2020-09-08 09:43:34 +0200",
  Journal       = "Mathematische Zeitschrift",
  Number        = "2",
  Pages         = "176---210",
  Title         = {Untersuchungen {\"u}ber das logische Schlie{\ss}en. I},
  Volume        = "39",
  Year          = "1934"
}

@Article{ Gentzen:1934, Author = "Gentzen, Gerhard", date-added = "2020-09-08 09:42:50 +0200", date-modified = "2020-09-08 09:43:34 +0200", Journal = "Mathematische Zeitschrift", Number = "2", Pages = "176---210", Title = {Untersuchungen {\"u}ber das logische Schlie{\ss}en. I}, Volume = "39", Year = "1934" }