Technically you can't compare two countable sets using the Lebesgue measure, because they will both have measure 0. EDIT: You could instead say something like

Technically you can't compare two countable sets using the Lebesgue measure, because they will both have measure 0. EDIT: You could instead say something like 'the useful reals are an infinite-degree field extension of the rationals'. (Although as I mentioned elsewhere it's actually impossible to define the useful reals.)