
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 four propositions:  
①$$a+b≥2 \sqrt {ab}$$;      
②$$\sin^{2}x+ \frac {4}{\sin^{2}x}≥4$$;  
③Let x and y be positive numbers, if $$\frac {1}{x}+ \frac {9}{y}=1$$, then the minimum value of x+y is 12;  
④If $|x-2|<\varepsilon$, $|y-2|<\varepsilon$, then $|x-y|<2\varepsilon$.  
The sequence numbers of all true propositions are \_\_\_\_\_\_.

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