Let $H$ be a Hilbert space.
Suppose the following holds: for every orthonormal basis $\{e_n\}$ of $H$ and sequence $\{\epsilon_n\} \in \ell^2(\mathbb{N})$, with $C:= \prod_n [-\epsilon_n e_n, \epsilon_n e_n ]$, if $\nu$ denotes the product measure $dx/2\epsilon_n$, then $\nu((H\backslash A) \cap C) = 0$.
Then $H\backslash A$ is called a negligible set.
Is there a technical term for this type of set? I want to know more details about it but no clue what to search for. Thanks.
