KulpaW., PlewikS., and TurzańskiM. “Bolzano-Weierstrass Principle of Choice Extended towards Ordinals”. Annales Mathematicae Silesianae, Vol. 17, Sept. 2003, pp. 9-16, https://www.journals.us.edu.pl/index.php/AMSIL/article/view/14097.