
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 The negation of the proposition "For all $x \in \mathbb{R}, x^2 \geq 0$" is "There exists an $x \in \mathbb{R}, x^2 \leq 0$";  
② The closer the absolute value of the correlation coefficient $r$ is to 1, the stronger the degree of linear correlation between the two variables;  
③ If $n \subset a$ and $m \parallel n$, then $m \parallel a$;  
④ "$a= \frac {2}{5}$" is the necessary and sufficient condition for "The line $ax+2y+3a=0$ and the line $3x+(a-1)y+7-a=0$ to be perpendicular to each other."  
The sequence numbers of the true propositions are __________. (Please fill in the sequence numbers of all true propositions)

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