Implicit definability and compactness in infinitary languages -- Some remarks on the model theory of infinitary languages -- Remarks on the theory of geometrical constructions -- Note on admissible ordinals -- An algebraic proof of the barwise compactness theorem -- Formulas with linearly ordered quantifiers -- Some problems in group theory -- Choice of infinitary languages by means of definability criteria; Generalized recursion theory -- Definability, automorphisms, and infinitary languages -- The hanf number for complete sentences -- Quantified algebras -- Normal derivability in classical logic -- A determinate logic -- (?1, ?) properties of unions of models.