
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
Proposition: ① The larger the observed value of $K^2$, the greater the possibility that "x is not related to y". ② The larger the variance of residuals $S^2$, the better the fitting effect of the regression line. ③ The larger $R^2$ is, the better the degree of fit. Therefore, the correct proposition number is.

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