
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
Given that α and β are two distinct planes, consider the following four conditions:  
① There exists a line a such that a is perpendicular to α and a is also perpendicular to β;  
② There exists a plane γ such that γ is perpendicular to α and γ is also perpendicular to β;  
③ There exist two parallel lines a and b where a is contained in α, b is contained in β, and each is parallel to the other's plane (a∥β and b∥α);  
④ There exist two skew lines a and b where a is contained in α, b is contained in β, and each is parallel to the other's plane (a∥β and b∥α).  
Among these, the sufficient conditions for plane α to be parallel to plane β are denoted by ____________. (Fill in all applicable sequence numbers)

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