On automorphisms of algebras with a single unary operation Fuhrken, G. — 1973 Portugaliae mathematica
Skolem-type normal forms for first-order languages with a generalized quantifier G. Fuhrken — 1964 Fundamenta Mathematicae
A finitely Axiomatizable complete theory with atomless F1 (T). A. Ehrenfeucht; Fuhrken — 1971 Archiv für mathematische Logik und Grundlagenforschung