Consider the following system of equations depending on the real parameter a:
$$\left. \begin{array} { l } x + a y + z = a + 1 \\ - a x + y - z = 2 a \\ - y + z = a \end{array} \right\}$$
It is requested:\ a) (2 points) Discuss the system according to the different values of a.\ b) (0.5 points) Solve the system for $\mathrm { a } = 0$.