Of course, whether a number is definable or not depends on the surrounding theory. Stick to first-order theory of the reals and only algebraic numbers will be definable! Definable in ZF? Or what?
EDIT Apr 30: Oops! Obviously definability depends only on the ambient language, not the actual ambient theory… no difference here between ZF and ZFC...
Of course, whether a number is definable or not depends on the surrounding theory. Stick to first-order theory of the reals and only algebraic numbers will be definable! Definable in ZF? Or what?
EDIT Apr 30: Oops! Obviously definability depends only on the ambient language, not the actual ambient theory… no difference here between ZF and ZFC...