I got the following statement:
For each set $N \subseteq \mathbb R^n$ with cardinality of the continuum $\#N=\mathfrak c$ there is a subset $M \subseteq N$ with $M \notin \mathcal B(\mathbb R^n)$.
Can somebody tell me why this is true? I thought of different cardinalities, but that doesn't seem to work out.. Thanks in advance!