[2] P. R. Halmos: 
Measure Theory. D. van Nostrand Comp., Inc., Toronto, New York, London 1951. 
MR 0033869 
[3] H.  Rasiowa R. Sikorski: 
The  Mathematics of Metamathematics. Third Edition, PWN, Warszawa 1970. 
MR 0344067 
[4] R. Sikorski: 
Boolean Algebras. Second Edition, Springer Verlag, Berlin-Göttingen-Heidelberg-New York 1964. 
Zbl 0123.01303