A calculus for finitely satisfiable formulas with identity. Arthur M. Bullock; Hubert H. Schneider — 1972 Archiv für mathematische Logik und Grundlagenforschung
Semantics of the predicate calculus with identity and the validity in the empty individual-domain Schneider, Hubert H. — 1958 Portugaliae mathematica
A syntactical characterization of the predicate calculus with identity and the validity in all individual-domains Schneider, Hubert H. — 1961 Portugaliae mathematica