Well, the kata description says 'The string has a length greater or equal to one and contains only letters from a-z'?

I'm a novice to the workings of 'auto', so in this case does the compiler deduce the type by using the return type of "length()"?

Thank you!

This solution is incorrect. It could be that the test cases provided are not good, but (for example) capital letters are not shown as an error as they should be. Or anything less than 'a' for that matter.

Not true. If you use auto you're just letting the compiler do the type deduction.

making denum and numer auto is bad practice because that forces them to be instantiated at run-time instead of compile. if you know the type use it.