I'm using Rails 5. I want to know if a varaible (which you can assume is a String) contains at least one letter (upper case or lower case). However, I don't want to use regular expressions (I've noticed if the encoding is not UTF-8, regular expressiosn tend to crash). So I'm wondering how I can check if a string hast at least one letter.

THis doesn't work

```
input.downcase.include?("abcdefghijklmnopqrstuvwxyz")

```