On this page : https://en.wikipedia.org/wiki/Complete_measure
one can find that:
I am surprised by the paragraph talking about the vitali set. How on earth can you take :
$$ \lambda^2 ( \{0\} \times A) $$
when $$ A \notin \mathcal B $$
I believe, one can only take sets in $ \mathcal B \times \mathcal B$ or do I misunderstand something ?
any idea is welcomed, thanks.