
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 that $a$, $b$, $l$ represent three different lines in space, and $α$, $β$, $γ$ represent three different planes in space, the sequence number of the correct proposition among the following four propositions is______.

$①$ If $a ⊥ α$, $b ⊥ β$, $l ⊥ γ$, and $a // b // l$, then $α // β // γ$;

$②$ If $α ⊥ γ$, $β ⊥ γ$, and $α ∩ β = l$, then $l ⊥ γ$;

$③$ If $a ⊂ α$, $b ⊂ β$, $α ∩ β = a$, $l ⊥ a$, $l ⊥ b$, then $l ⊥ β$;

$④$ If $a$ and $b$ are skew lines, $a ⊥ α$, $b ⊥ β$, $l ⊥ a$, $l ⊥ b$, $l ⊄ α$, $l ⊄ β$, then $α$ intersects with $β$, and the intersection line is parallel to $l$.

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