
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
Given the following statements:  
① For all $a, b \in \mathbb{R}$, the equation $ax+b=0$ has exactly one solution;  
② The truth of $q \lor p$ is a necessary condition for the truth of $p \land q$;  
③ The contrapositive of the statement "If $a$ and $b$ are both even, then $a+b$ is even" is "If $a+b$ is not even, then $a$ and $b$ are not both even";  
④ For the statement $p$: There exists an $x \in \mathbb{R}$ such that $\sin x \leq 1$, the negation $\lnot p$ is $\forall x \in \mathbb{R}, \sin x > 1$.  
Among these, the correct statements are numbered as follows:

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