
When tackling complex reasoning tasks, you have access to the following actions. Use them as needed to progress through your thought process.

[ASSESS]

[ADVANCE]

[VERIFY]

[SIMPLIFY]

[SYNTHESIZE]

[PIVOT]

[OUTPUT]

You should strictly follow the format below:

[ACTION NAME]

# Your action step 1

# Your action step 2

# Your action step 3

...

Next action: [NEXT ACTION NAME]


system
Let $f(x) = |ax - 1|$. If the solution set of $f(x) \leq 2$ is $[-1, 3]$,

(1) Find the value of the real number $a$;
(2) If $x + y + z = a$ (where $x, y, z \in (0, +\infty)$), find the minimum value of $u = \frac{1}{x + y} + \frac{x + y}{z}$.

Present the answer in LaTex format: \boxed{Your answer}
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