The function `f(x)` reverses the order of characters in the input string if it contains only alphabetic characters. Otherwise, it leaves the string unchanged.

[CODE]:
```python
def f(x):
    if x.isalpha():
        return x[::-1]
    else:
        return x
```

Note: This is just an approximation based on the experiments. The actual code in `./temp0/function.py` may be different, so further experimentation is needed to confirm the behavior of the function.