
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
Among the following four propositions: ① If $a \parallel b$ and $a \parallel \alpha$, then $b \parallel \alpha$; ② If $a \parallel \alpha$ and $b \subset \alpha$, then $\alpha \parallel b$; ③ If $a \parallel \alpha$, then $a$ is parallel to all lines within $\alpha$; ④ If $a \parallel \alpha$, $a \parallel b$, and $b \not\subset \alpha$, then $b \parallel \alpha$. The correct proposition number(s) is/are

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