Erdős, P. and Silverman, R. and Stein, A., Intersection properties of families containing sets of nearly the same size. Ars Combin. (1983), 247-259.

Erdős, P., On the combinatorial problems which I would most like to see solved. Combinatorica (1981), 25-42.

Various, Some of Paul's favorite problems. Booklet produced for the conference "Paul Erdős and his mathematics", Budapest, July 1999 (1999).