
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
The serial numbers for true propositions among the following are:
① The inverse of the proposition "Congruent triangles have equal area";
② The negation of the proposition "If $ab=0$, then $a=0$";
③ The contrapositive of the proposition "All angles in an equilateral triangle are $60^\circ$".
Fill in the serial numbers of all the true propositions on the line.

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