1. Infinitary logic and admissible sets;Barwise,1967
2. Relative characterizability and generalized existential quantifiers;Craig;Notices Am. Math. Soc.,1962
3. On the logic with the added quantifier Q (there are uncountably many);Ebbinghaus;Notices Am. Math. Soc.,1968
4. Models of axiomatic theories admitting automorphisms;Ehrenfeucht;Fund. Math.,1956