
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 Cutting a pyramid with a plane parallel to its base, the part between the base and the section is called a frustum;  
② The lateral edges of a frustum, when extended, must intersect at a point;  
③ A cone can be considered as a right-angled trapezoid rotating around the line containing its leg perpendicular to the base, with the other three sides forming the curved surface;  
④ A hemisphere rotating around the line of its diameter forms a sphere.  
The correct propositions are     .

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