
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 $n$ lines ($n\geqslant 3$) in a plane, where exactly two lines are parallel and no three lines intersect at the same point. Let $f(n)$ denote the number of intersection points of these $n$ lines. Determine $f(4)=\_\_\_\_\_\_$ and express $f(n)=\_\_\_\_\_\_(n$ in terms of $n$ when $n > 4$.

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