(4) Solve the inequality $|x-1|<x+a$ for $x$, where the constant $a \in \mathbf{R}$
(4) When $a \leqslant -1$, the solution set is $\varnothing$; when $a > -1$, the solution set is
$$
\left(\frac{1-a}{2},+\infty\right)
$$