
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 one is (fill in the serial number):  
① A prism cut by any plane is divided into two parts, both of which are prisms;  
② All lateral faces of a frustum are isosceles trapezoids;  
③ Cutting a cone with a plane results in a geometry of a cone and a frustum;  
④ Cutting a sphere with any plane results in a cross-section that is a circular surface.

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