
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 $f(x)=\lg (x+ \sqrt {x^{2}+1})+x$, if $f(1+a)+f(1-a^{2}) < 0$, then the range of $a$ is \_\_\_\_\_\_ .

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