
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
Xiao Mahu made a mistake when calculating the difference between a polynomial and $2a^{2}+a-5$ by forgetting to put parentheses around the two polynomials. As a result, the signs of the last two terms were not changed, and the obtained difference is $a^{2}+3a-1$.  
$(1)$ Find this polynomial.  
$(2)$ Calculate the correct result of this problem.

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