Sure, I can help you write a test case generator for the "Set Difference" problem. Here is the Python code for generating the test cases:

```python
import random

def generate_sorted_unique_list(size, max_value):
    """Generates a sorted list of unique integers."""
    return sorted(random.sample(range(max_value + 1), size))

def tcgen():
    # Define the constraints
    n = random.randint(1, 200000)
    m = random.randint(1, 200000)
    
    # Generate two sorted unique lists
    A = generate_sorted_unique_list(n, 10**9)
    B = generate_sorted_unique_list(m, 10**9)
    
    return n, A, m, B

# Example of using the test case generator
if __name__ == "__main__":
    n, A, m, B = tcgen()
    print(n)
    print(' '.join(map(str, A)))
    print(m)
    print(' '.join(map(str, B)))
```

### Explanation

1. **generate_sorted_unique_list(size, max_value)**:
   - This function generates a sorted list of unique integers. The `random.sample` function is used to generate a list of unique integers, and then the list is sorted.

2. **tcgen()**:
   - Randomly generates the sizes `n` and `m` for the sets `A` and `B` within the given constraints.
   - Uses the `generate_sorted_unique_list` function to generate the sorted lists `A` and `B`.

3. **Main Section**:
   - This part runs the test case generator and prints the generated test case in the required format.

This generator will help you create valid test cases for the "Set Difference" problem. You can adjust the print statements or store the generated data as needed for your testing framework.