
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
Let $a$ and $b$ be two non-coincident planes, and let $l$, $m$, $n$ be three mutually non-coincident lines. Consider the following four statements:  
1. If plane $a$ is parallel to plane $b$, and line $l$ lies in plane $a$, then line $l$ is parallel to plane $b$.
2. If line $m$ lies in plane $a$, line $n$ lies in plane $a$, line $m$ is parallel to plane $b$, and line $n$ is parallel to plane $b$, then plane $a$ is parallel to plane $b$.
3. If line $l$ is parallel to plane $a$ and line $l$ is perpendicular to plane $b$, then plane $a$ is perpendicular to plane $b$.
4. If lines $m$ and $n$ are skew lines, line $m$ is parallel to plane $a$, line $n$ is parallel to plane $a$, and line $l$ is perpendicular to line $m$ and line $n$, then line $l$ is perpendicular to plane $a$.

The sequence numbers of the true statements are __★__.

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