Please solve the programming task below using a self-contained code snippet in a markdown code block.

You are given a string s representing a list of words. Each letter in the word has one or more options.

If there is one option, the letter is represented as is.
If there is more than one option, then curly braces delimit the options. For example, "{a,b,c}" represents options ["a", "b", "c"].

For example, if s = "a{b,c}", the first character is always 'a', but the second character can be 'b' or 'c'. The original list is ["ab", "ac"].
Return all words that can be formed in this manner, sorted in lexicographical order.
 
Please complete the following python code precisely:
```python
class Solution:
    def expand(self, s: str) -> List[str]:
```