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.