
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
If the function $f(x)$ is a monotonic function on its domain $D$, and there exists an interval $[a,b] \subseteq D$ (where $a < b$), such that when $x \in [a,b]$, the range of $f(x)$ is exactly $[a,b]$, then the function $f(x)$ is called a wonderful function on $D$. If the function $g(x) = x^2 + m$ is a wonderful function on $(-\infty, 0)$, then the range of the real number $m$ is ______.

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