Kalemba, Piotr, and Andrzej Kucharski. “Universally Kuratowski–Ulam Spaces and Open-Open Games”. Annales Mathematicae Silesianae, vol. 29, Sept. 2015, pp. 85-92, https://trrest.vot.pl/ojsus/index.php/AMSIL/article/view/13979.