Baire one star function

A Baire one star function is a type of function studied in real analysis. A function ${\displaystyle f:\mathbb {R} \to \mathbb {R} }$ is in class Baire* one, written ${\displaystyle f\in \mathbf {B} _{1}^{*}}$, and is called a Baire one star function, if for each perfect set ${\displaystyle P\in \mathbb {R} }$, there is an open interval ${\displaystyle I\in \mathbb {R} }$, such that ${\displaystyle P\cap I}$ is nonempty, and the restriction ${\displaystyle f|_{P\cap I}}$ is continuous. The notion seems to have originated with B. Kirchheim in an article titled 'Baire one star functions' (Real Anal. Exch. 18 (1992/93), 385-399). The terminology is actually due to Richard O'Malley, 'Baire* 1, Darboux functions' Proc. Amer. Math. Soc. 60 (1976) 187-192. The concept itself (under a different name) goes back at least to 1951. See H. W. Ellis, 'Darboux properties and applications to nonabsolutely convergent integrals' Canad. Math. J., 3 (1951), 471-484, where the same concept is labelled as [CG] (for generalized continuity).

External links

• A paper which defines class Baire* one