
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 sets $A$ and $B$ are subsets of the universal set $U = \{1, 2, 3, 4\}$, and $\complement_U(A \cup B) = \{4\}$, $B = \{1, 2\}$, then $A \cap (\complement_U B) = \quad$.

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