
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 statements: ① Two points determine a line; ② The shortest distance between two points is a straight line; ③ If $|a| = -a$, then $a < 0$; ④ If $a$ and $b$ are opposite numbers, then the quotient of $a$ and $b$ must be equal to $-1$. The correct ones are. (Please fill in the serial number)

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