
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
Given $f(x)=e^{x}-ax-1$.

$(1)$ If $f(x)$ is monotonically increasing in its domain $\mathbb{R}$, find the range of values for $a$;

$(2)$ Does there exist a real number $a$ such that $f(x)$ is monotonically decreasing on $(-\infty,0]$ and monotonically increasing on $[0,+\infty)$? If it exists, find the value of $a$; if not, explain why.

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