f=\cases {-1-x+x-2, &$x\le -1$ \cr x+1+x-2, &$-1< x\le 2$\cr x+1-x+2, &$x> 2$ \cr} = \cases{-3, &$x\le -1$ \cr 2x-1, &$-1< x\le 2$\cr 3, &$x>2\cr$}