
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 line $l_1$: $(a-1)x-4y=1$, line $l_2$: $(a+1)x+3y=2$, and line $l_3$: $x-2y=3$.

(1) If the slope angle of line $l_1$ is 135°, find the value of the real number $a$;  
(2) If $l_2 \parallel l_3$, find the value of the real number $a$.

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