$\{ 2x | x\in \mathbb{N}\}=\{2,4,6,8,10,\cdots\}$ $\{2x+1| x\in \mathbb{N}\}=\{3,5,7,\cdots\}$ $W=\{0,1,2,3,\cdots\}$ $\{2x-1| x\in \mathbb{W}\}=\{-1,1,3,\cdots\}$ $\{ 2x+1| x\in \mathbb{W}\}=\{1,3,5,\cdots\}$