
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, the correct ones are \_\_\_\_\_\_. (Fill in the serial numbers of the correct propositions)  
① To characterize the regression effect using $R^2=1- \frac{\sum\limits_{i=1}^{n}(y_{i}- \hat{y}_{i})^{2}}{\sum\limits_{i=1}^{n}(y_{i}- \bar{y})^{2}}$, the larger the $R^2$, the worse the model's fitting effect; conversely, the better;  
② If a differentiable function $f(x)$ attains an extremum at $x=x_0$, then $f′(x_0)=0$;  
③ Inductive reasoning is reasoning from specific to general, while deductive reasoning is from general to specific;  
④ In mathematics, the synthetic method of proving problems is "from cause to effect", while the analytic method is "from effect to cause".

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