
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 that the arithmetic sequence $\{a_n\}$ has a common difference of $2$, and the sum of the first $n$ terms is denoted as $S_n$, such that $S_1$, $S_2$, $S_4$ form a geometric sequence,  
(Ⅰ) Find the general formula for the $n$-th term of $\{a_n\}$;  
(Ⅱ) Let $b_n=(-1)^{n-1} \frac {4n}{a_{n}a_{n+1}}$, calculate the sum of the first $n$ terms of $\{b_n\}$, denoted as $T_n$.

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