
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, the correct proposition number is  
① The negation of the proposition "If $x^2 = 1$, then $x = 1$" is "If $x^2 = 1$, then $x \neq 1$";  
② The negation of the proposition "There exists an $x \in \mathbb{R}$ such that $x^2 + x - 1 < 0$" is "For all $x \in \mathbb{R}, x^2 + x - 1 > 0$";  
③ The contrapositive of the proposition "If $x = y$, then $\sin x = \sin y$" is a false statement;  
④ If "p or q is a true proposition, then at least one of p, q is true".

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