1. These sets were constructible in a technical sense far too broad to render them acceptable to constructivist mathematicians such as Borel and Lebesgue. In particular, the definition of constructible set presupposed all the transfinite ordinals (see 4.10).
2. Janiszewski’s article is translated in Kuzawa 1968, 112–118. For a detailed account of the rise of the Warsaw school, see especially Kuratowski 1980 and Kuzawa 1968, but also Kura-towski 1975 and Sierpiński 1959.
3. Sierpiński 1963, 27. On the origin of this journal, see also Kuzawa 1970. Lebesgue encouraged the journal but feared that its scope was too narrow [1922a, 36]. He used its pages to publish his own research as well as to reiterate his arguments against the Axiom [1921, 259–260].
4. This was shown by Jaegermann [1965], using Cohen’s method.
5. Sierpiński 1917.