
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 line $a$, $b$ and plane $\alpha$, the correct proposition number is \_\_\_\_\_\_.
$①$ If $a//\alpha$, $b\subset\alpha$, then $a//b$;
$②$ If $a//\alpha$, $b//\alpha$, then $a//b$;
$③$ If $a//b$, $b\subset\alpha$, then $a//\alpha$;
$④$ If $a//b$, $b\subset\alpha$, then $a//\alpha$ or $a\subset\alpha$.

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