
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 propositions:
① All acute angles are equal;
② The perpendicular segment is the shortest;
③ Complementary angles are adjacent angles;
④ In the same plane, if $L_1 \perp L_2$ and $L_1 \perp L_3$, then $L_2 \parallel L_3$,
the true propositions are     . (Fill in the correct serial numbers)

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