
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, fill in the numbers of all true propositions.  
① The necessary condition for "A∩B=A" to hold is "A⊊B";  
② The negation of "If $x^2+y^2=0$, then both x and y are 0";  
③ The converse of "Congruent triangles are similar triangles";  
④ The contrapositive of "The opposite angles of a cyclic quadrilateral are supplementary".

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