
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
The derivative of the function $f(x)$ is denoted as $f'(x)$. If for any $x_{1}, x_{2} (x_{1} \neq x_{2})$ in the domain, the equation $\frac{f(x_{1})-f(x_{2})}{x_{1}-x_{2}}=f'\left(\frac{x_{1}+x_{2}}{2}\right)$ always holds, then $f(x)$ is called a constant mean variation function. Given the following functions:  
1. $f(x)=2x+3$;  
2. $f(x)=x^{2}-2x+3$;  
3. $f(x)=\frac{1}{x}$;  
4. $f(x)=e^{x}$;  
5. $f(x)=\ln x$.  

The numbers of the functions that are constant mean variation functions are __________. (Write down the numbers of all functions that meet the condition)

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