
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
Consider the following four propositions:
1. Two unit vectors must be equal.
2. If vectors $\overrightarrow{a}$ and $\overrightarrow{b}$ are not collinear, then both $\overrightarrow{a}$ and $\overrightarrow{b}$ are non-zero vectors.
3. The zero vector has no direction.
4. Two equal vectors must have identical starting and ending points.

Identify the correct proposition(s): _______ (fill in the sequence number).

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