
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 the function $f(x)=x^{3}-ax-1$.

$(1)$ If $f(x)$ is an increasing function on $\mathbb{R}$, find the range of the real number $a$;

$(2)$ If the function $f(x)$ is a decreasing function on $(-1,1)$, find the range of the real number $a$;

$(3)$ If the decreasing interval of the function $f(x)$ is $(-1,1)$, find the value of the real number $a$;

$(4)$ If the function $f(x)$ is not monotonic on the interval $(-1,1)$, find the range of the real number $a$.

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