
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
Let lines a and b have direction vectors $\overrightarrow {e_{1}}$ and $\overrightarrow {e_{2}}$ respectively, and let plane α have a normal vector $\overrightarrow {n}$. Then among the following inferences:  
① If $\overrightarrow {e_{1}}\parallel \overrightarrow {e_{2}}$ and $\overrightarrow {e_{1}}\parallel \overrightarrow {n}$, then b is parallel to α.   
② If $\overrightarrow {e_{1}}\parallel \overrightarrow {n}$ and $\overrightarrow {e_{2}}\parallel \overrightarrow {n}$, then a is parallel to b.  
③ If $\overrightarrow {e_{1}}\parallel \overrightarrow {n}$, b is not contained in α, and $\overrightarrow {e_{1}}$ is perpendicular to $\overrightarrow {e_{2}}$, then b is parallel to α.  
④ If $\overrightarrow {e_{1}}\parallel \overrightarrow {e_{2}}$ and $\overrightarrow {e_{1}}\parallel \overrightarrow {n}$, then b is perpendicular to α.  
Identify the correct proposition(s).

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