
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
Proposition:<br/>①Vertical angles are equal;<br/>②Corresponding angles are equal;<br/>③If $ab=1$, then $a=1$ or $b=1$;<br/>④The number whose square is equal to $4$ is $2$.<br/>Among them, the true propositions are ______$(Fill in the numbers)$.

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