(4) When the real number $a \in$ $\qquad$, there does not exist a real number $x$ such that $|x+a+1|+|x+$ $a^{2}-2|<3$.
(4) $(-\infty,-2] \cup[0,1] \cup[3, \infty)$ Hint: No solution $\Leftrightarrow \mid a^{2}-$ a) $-3 \mid \geqslant 3 \Leftrightarrow a^{2}-a \leqslant 0$ or $a^{2}-a-6 \geqslant 0$.