Editing Wacław Sierpiński (section)

==Career==
[[File:Sierpinski square.png|thumb|left|Sierpinski square, a [[fractal]]]]

In 1907 Sierpiński first became interested in [[set theory]] when he came across a theorem which stated that points in the plane could be specified with a single coordinate. He wrote to [[Tadeusz Banachiewicz]] (then at [[Georg August University of Göttingen|Göttingen]]), asking how such a result was possible. He received the one-word reply '[[Georg Cantor|Cantor]]'. Sierpiński began to study [[set theory]] and, in 1909, he gave the first ever lecture course devoted entirely to the subject.<ref name="Paulina Rowińska"/>

Sierpiński maintained an output of research papers and books. During the years 1908 to 1914, when he taught at the University of [[Lwów]], he published three books in addition to many research papers. These books were  ''The Theory of Irrational Numbers'' (1910), ''Outline of Set Theory'' (1912), and ''The Theory of Numbers'' (1912).

[[File:Wacław Siepiński grave.JPG|thumb|Grave of Wacław Sierpiński]]

When [[World War I]] began in 1914, Sierpiński and his family were in [[Russia]]. To avoid the persecution that was common for [[Poland|Polish]] foreigners, Sierpiński spent the rest of the war years in [[Moscow]] working with [[Nikolai Luzin]]. Together they began the study of [[analytic set]]s. In 1916, Sierpiński gave the first example of an [[normal number|absolutely normal number]].<ref>{{Cite web |url=https://mathshistory.st-andrews.ac.uk/Biographies/Sierpinski/#:~:text=In%201916%2C%20during%20his%20time%20in%20Moscow%2C%20Sierpi%C5%84ski,I%20ended%20in%201918%2C%20Sierpi%C5%84ski%20returned%20to%20Lemberg. |title=Wacław Sierpiński |website=mathshistory.st-andrews.ac.uk |access-date=27 April 2023}}</ref>

When [[World War I]] ended in 1918, Sierpiński returned to [[Lwow|Lwów]]. However shortly after taking up his appointment again in [[Lviv|Lwów]] he was offered a post at the [[Warsaw University|University of Warsaw]], which he accepted. In 1919 he was promoted to a [[professor]]. He spent the rest of his life in [[Warsaw]].<ref>{{Cite web |url=https://www.polskieradio.pl/39/156/Artykul/1738959,Waclaw-Sierpinski-Badacz-zagadek-nieskonczonosci |language=pl |title=Wacław Sierpiński. Badacz zagadek nieskończoności |website=polskieradio.pl |access-date=27 April 2023}}</ref>

During the [[Polish–Soviet War]] (1919–1921), Sierpiński helped break [[Russian SFSR|Soviet Russia]]n [[cipher]]s for the [[Poland|Polish]] [[General Staff]]'s [[Cipher Bureau (Poland)|cryptologic agency.]]

In 1920, Sierpiński, together with [[Zygmunt Janiszewski]] and his former student [[Stefan Mazurkiewicz]], founded the mathematical journal ''[[Fundamenta Mathematicae]]''.<ref name="Wacław Sierpiński (1882-1969)" /> Sierpiński edited the journal, which specialized in papers on [[set theory]].

During this period, Sierpiński worked predominantly on [[set theory]], but also on [[point set topology]] and [[function (mathematics)|function]]s of a [[Function of a real variable|real variable]]. In [[set theory]] he made contributions on the [[axiom of choice]] and on the [[continuum hypothesis]]. He proved that [[Zermelo–Fraenkel set theory]] together with the [[Generalized continuum hypothesis]] imply the [[Axiom of choice]]. He also worked on what is now known as the [[Sierpiński curve]]. Sierpiński continued to collaborate with Luzin on investigations of analytic and projective sets. His work on [[function (mathematics)|function]]s of a [[Function of a real variable|real variable]] includes results on [[functional series]], [[differentiability]] of functions and [[Baire's classification]].

Sierpiński worked at the [[Institute of Mathematics of the Polish Academy of Sciences|State Institute of Mathematics]], which was incorporated into the [[Polish Academy of Sciences]] in 1952.<ref>{{Cite web |url=https://www.impan.pl/en/insitute/about-us/history |title=History |website=impan.pl |access-date=7 December 2024}}</ref> He retired in 1960 as [[professor]] at the [[Warsaw University|University of Warsaw]], but continued until 1967 to give a seminar on the [[Number theory|Theory of Numbers]] at the [[Polish Academy of Sciences]]. He also continued editorial work as editor-in-chief of ''[[Acta Arithmetica]]'', and as a member of the editorial board of ''[[Rendiconti del Circolo Matematico di Palermo]]'', ''Composito Matematica'', and ''[[Zentralblatt MATH|Zentralblatt für Mathematik]]''.

In 1964 he was one of the signatories of the so-called [[Letter of 34]] to Prime Minister [[Józef Cyrankiewicz]] regarding freedom of culture.<ref>{{Cite web |url=https://dzieje.pl/kultura-i-sztuka/list-34-pierwszy-duzy-protest-wobec-polityki-kulturalnej-wladz-prl |language=pl |title=List 34 - pierwszy duży protest wobec polityki kulturalnej władz PRL |website=dzieje.pl |date=10 March 2019 |access-date=27 April 2023}}</ref>

Sierpiński is interred at the [[Powązki Cemetery]] in [[Warsaw]], [[Poland]].<ref>{{Cite web |url=https://cmentarze.um.warszawa.pl/pomnik.aspx?pom_id=3806 |language=pl |title=Warszawskie Zabytkowe Pomniki Nagrobne |access-date=27 April 2023}}</ref>