
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 Hu, a student, is working on a problem. Given two polynomials $A$ and $B$, where $B=4x^{2}-3y-1$, calculate $A-B$. While calculating $A-B$, he mistakenly took it as $A+B$ and obtained the result $6x^{2}-y$. <br/>$(1)$ Find the polynomial $A$; <br/>$(2)$ If $|x-1|$ and $\left(y+1\right)^{2}$ are opposite in sign, find the value of $A-B$.

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