
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 $A=\left\{x \mid x^{2}+4x=0\right\}$, $B=\left\{x \mid x^{2}+2(a+1)x+a^{2}-1=0, x \in \mathbf{R}\right\}$. If $B \subseteq A$, find the range of the real number $a$.

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