
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
How many ways can two items be chosen from \( n \) items?

So far, the number of ways to choose:

2 items from \( n \) (or the number of options when 2 lamps are lit out of \( p \) lamps) is denoted by \( C_{n}^{2} \). The task is to calculate \( C_{n}^{2} \) (for example, in problem 56 it has been counted that \( C_{5}^{2}=10 \)).

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