@Article{         Gentzen:1935,
  Author        = "Gentzen, Gerhard",
  date-added    = "2020-09-08 09:44:17 +0200",
  date-modified = "2020-09-08 09:44:35 +0200",
  Journal       = "Mathematische Zeitschrift",
  Number        = "3",
  Pages         = "405---431",
  Title         = {Untersuchungen {\"u}ber das logische Schlie{\ss}en. II},
  Volume        = "39",
  Year          = "1935"
}

@Article{ Gentzen:1935, Author = "Gentzen, Gerhard", date-added = "2020-09-08 09:44:17 +0200", date-modified = "2020-09-08 09:44:35 +0200", Journal = "Mathematische Zeitschrift", Number = "3", Pages = "405---431", Title = {Untersuchungen {\"u}ber das logische Schlie{\ss}en. II}, Volume = "39", Year = "1935" }