
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 an arithmetic sequence $\{a_n\}$ with a common difference of 2, and the sum of the first $n$ terms is $S_n$, it is also known that $S_1$, $S_2$, and $S_4$ form a geometric sequence.  
(I) Determine the general formula for the sequence $\{a_n\}$.  
(II) Let $b_n = (-1)^{n-1} \frac {4n}{a_{n}a_{n+1}}$, find the sum of the first $n$ terms of the sequence $\{b_n\}$, denoted as $T_n$.

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