
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:  
① The larger the linear correlation coefficient $r$, the stronger the linear correlation between two variables; conversely, the weaker the linear correlation;  
② The smaller the sum of squared residuals of a model, the better the fitting effect;  
③ Using the correlation index $R^2$ to depict the regression effect, the smaller $R^2$ is, the better the model fitting effect;  
④ Random error $e$ is a measure of forecasting accuracy, and it satisfies $E(e)=0$.  
The correct ones are \_\_\_\_\_\_ (fill in the serial numbers).

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