First, define the sets:
S_n^k = \Big[\frac{k-1}{2^n}, \frac{k}{2^n}\Big]
From these intervals, define the sequence of functions:
f_n^k = \chi_{S_n^k}(x) + \chi_{S_n^k}(-x)
Where for each n to progress +1, k must sweep from 1 to 2^n + 1.
Certainly, for every n,
\int_{\mathbb{R}} f_n^k = \frac{1}{2^{n-1}}
Since the collection of functions \lbrace f_n^k \rbrace is countable, with a well-defined sequence, let us just enumerate them with the single index m. We have:
\int_{\mathbb{R}} |f_m - 0| = \int_{\mathbb{R}} f_m \to 0
However, for any x \in \mathbb{R}, it's clear that \lim_{m\to \infty} f_m(x) does not exist.
To expand this to \mathbb{R}^d, just replace the intervals with a closed balls centered at the origin subtracting open balls with the same dyadic rational-difference... (onion-layers).
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