Functions

If a real valued function $f:[-1,2] \rightarrow B$ defined by

$$ f(x)= \begin{cases}1-x, & \text { when }-1 \leq x \leq 1 \\ x-1, & \text { when } 1 < x \leq 2\end{cases} $$

is a surjection, then $B=$