1. Introduction to Mathematical Logic;Mendelson,1964
2. Arithmetical Extensions of Relational Systems;Tarski;Comp. Math.,1957
3. Imcompleteness in Languages with Infinitely Long Expressions;Hanf;Fund. Math.,1964
4. Languages with Expressions of Infinite Length;Karp,1964
5. Some Remarks on Infinitely Long Formulas;Henkin,1961