
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
Simplify the following expression:

$$
\begin{aligned}
& 1+\frac{a_{1}}{1-a_{1}}+ \frac{a_{2}}{\left(1-a_{1}\right)\left(1-a_{2}\right)}+\frac{a_{3}}{\left(1-a_{1}\right)\left(1-a_{2}\right)\left(1-a_{3}\right)}+ \\
& \frac{a_{4}-a_{1}}{\left(1-a_{1}\right)\left(1-a_{2}\right)\left(1-a_{3}\right)\left(1-a_{4}\right)}
\end{aligned}
$$

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