The function converts lowercase letters to uppercase letters and shifts alphabetical characters by 3 positions forward in the alphabet (wrapping around at Z). If a character is not a lowercase letter or an uppercase letter, it remains unchanged.

[CODE]: 
```python
def f(x):
    result = ""
    for char in x:
        if char.islower():
            char = char.upper()
            shift_value = 3
            char = chr(((ord(char) - 65 + shift_value) % 26) + 65)
        result += char
    return result
```