Sure, here's the properly formatted code within a code block with Python syntax highlighting:

````python
elif a[1] in ["3", "4"]:
```

As for an example where this could be useful, imagine you are writing a program to process user input. The user is supposed to enter a number between 1 and 10, and your program needs to check if the input is valid. Instead of writing a long conditional statement with many OR operators to check if the input is equal to 1, 2, 3, 4, 5, 6, 7, 8, 9, or 10, you can use the in operator to check if the input is in a list of valid values:

```python
user_input = input("Enter a number between 1 and 10: ")
if user_input in ["1", "2", "3", "4", "5", "6", "7", "8", "9", "10"]:
    print("Valid input")
else:
    print("Invalid input")
```

This code checks if the user input is in the list of valid values using the in operator. If the input is valid, the program will print "Valid input". Otherwise, it will print "Invalid input". This approach is more concise and easier to read than using a long conditional statement with many OR operators.
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