Skip to main content
added 197 characters in body
Source Link
Robert Israel
  • 54.2k
  • 1
  • 76
  • 152

Let $h$ be the indicator function of the rationals. This is of Baire class 2, i.e. it is not the pointwise limit of a sequence of continuous functions, but it is the pointwise limit of a sequence of pointwise limits of continuous functions. For example, let $r_1, r_2, \ldots$ be an enumeration of the rationals, $g_n(x)$ the indicator function of $S_n = \{r_1, r_2, \ldots, r_n\}$, and $f_{ij}(x) = \exp(-i \;\text{dist}(x, S_j))$.

Let $h$ be the indicator function of the rationals. This is of Baire class 2, i.e. it is not the pointwise limit of a sequence of continuous functions, but it is the pointwise limit of a sequence of pointwise limits of continuous functions.

Let $h$ be the indicator function of the rationals. This is of Baire class 2, i.e. it is not the pointwise limit of a sequence of continuous functions, but it is the pointwise limit of a sequence of pointwise limits of continuous functions. For example, let $r_1, r_2, \ldots$ be an enumeration of the rationals, $g_n(x)$ the indicator function of $S_n = \{r_1, r_2, \ldots, r_n\}$, and $f_{ij}(x) = \exp(-i \;\text{dist}(x, S_j))$.

Source Link
Robert Israel
  • 54.2k
  • 1
  • 76
  • 152

Let $h$ be the indicator function of the rationals. This is of Baire class 2, i.e. it is not the pointwise limit of a sequence of continuous functions, but it is the pointwise limit of a sequence of pointwise limits of continuous functions.