
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
(Choice between coordinate system and parametric equations) Given the lines $$l_{1}: \begin{cases} \left.\begin{matrix}x=1-2t \\ y=2+kt.\end{matrix}\right.\end{cases}(t\text{ is the parameter})$$, $$l_{2}: \begin{cases} \left.\begin{matrix}x=s \\ y=1-2s.\end{matrix}\right.\end{cases}$$ (s is the parameter), if $l_{1}\parallel l_{2}$, then $k= \_\_\_\_\_\_$; if $l_{1}\perp l_{2}$, then $k= \_\_\_\_\_\_$.

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