# [Vyxal](https://github.com/Vyxal/Vyxal), 6 bytes
```
ka¦?Uc
```
[Try it Online!](https://vyxal.pythonanywhere.com/#WyIiLCIiLCJrYcKmP1VjIiwiIiwiYWJhY2FiYWRhYmFjYWJhIl0=)

```
ka¦    # prefixes of alphabet
     c # contains
   ?U  # Input uniquified
```