Gerald E. Sacks. Forcing with perfect closed sets. Axiomatic set theory, Proceedings of symposia in pure mathematics, vol. 13 part 1, American Mathematical Society, Providence, Rhode Island, 1971, pp. 331–355.
Joseph R. Shoenfield · Journal of Symbolic Logic · 1974
Gerald E. Sacks. Forcing with perfect closed sets. Axiomatic set theory, Proceedings of symposia in pure mathematics, vol. 13 part 1, American Mathematical Society, Providence, Rhode Island, 1971, pp. 331–355. - Volume 39 Issue 2