Infinite and finite sets : to Paul Erdo?s on his 60th birthday - Erdo?s, Paul, 1913-1996; Hajnal, A.; Rado, Richard, 1906-; So?s, Vera T.; Hanjnal, A.; Sos, Vera T.; Rado, R.; Erdos, Paul (Colloquia Mathematica Societatis Janos Bolyai (North Holland), 1975)