Given any (not necessarily finite) set $X$ as well as arbitrary subsets $A\subseteq X$ and $B\subseteq X$ if we know there exists a bijection $f:A\to B$ does this imply there exists a bijection $g:X\setminus A\to X\setminus B$?
I'm some what embarrassed to ask as it seems trivially true, though I am not totally certain.
Consider $A = \mathbb{R}$ and $B=\mathbb{R}\setminus\{0\}$ and $X=\mathbb{R}$. Then $|A|=|B|$, but $|X\setminus A|=0 \neq 1 = |X \setminus B|$.