A Baire function belongs to the smallest hierarchy of real-valued functions containing the continuous functions and closed under pointwise sequential limits.
A Baire class one function is a pointwise limit of continuous functions. On a complete metric domain, its set of discontinuities is meagre; in particular, it has a point of continuity on every nonempty perfect closed subset.
The indicator of the rational numbers in the real numbers is discontinuous everywhere because both the rationals and irrationals are dense. The discontinuity theorem for Baire class one functions therefore shows that it is not Baire class one.
Articles by others on the same topic
A Baire function is a specific type of function that arises in the field of descriptive set theory, which is a branch of mathematical logic and analysis. Baire functions are defined on the real numbers (or other Polish spaces) and can be categorized based on their levels of complexity. ### Definition: Baire functions are defined using the idea of Baire classes.