
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
If the line $$l_{1}: \begin{cases} x=1-2t \\ y=2+kt.\end{cases}$$ (where $t$ is a parameter) is perpendicular to the line $$l_{2}: \begin{cases} x=s \\ y=1-2s.\end{cases}$$ (where $s$ is a parameter), then $k=\boxed{-1}$.

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