
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 the following four propositions:  
① If sets A and B satisfy $A \cap B = A$, then $A \subseteq B$;  
② Given propositions p and q, if "p ∨ q" is true, then "p ∧ q" is true;  
③ Let $a$, $b$, $m \in \mathbb{R}$, if $a < b$, then $am^2 < bm^2$;  
④ If line $l_1: ax+y+1=0$ is perpendicular to line $l_2: x-y+1=0$, then $a=1$. The number of true propositions is     . (Write down the total number of true propositions)

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