(7) Given $A=\left\{x \mid x^{2}-1=0\right\}, B=\left\{y \mid y^{2}-2 a y+b=0, y \in \mathbf{R}\right\}$, if $B \subseteq$ $A$, and $B \neq \varnothing$, find the values of real numbers $a$ and $b$.
(7) $\left\{\begin{array}{l}a=1, \\ b=1\end{array}\right.$ or $\left\{\begin{array}{l}a=-1, \\ b=1\end{array}\right.$ or $\left\{\begin{array}{l}a=0, \\ b=-1\end{array}\right.$