which one

nice

God is in the little details...

ty @chrono79 i was wondering exactly the same thing as brazenAI

No need to be, every solution (unless it's absolute garbage like you YandereDev style developer) is alright tbh

i did something similar to that with a dict and exiting as soon as the value(number of appearance) of a key(letter) is more than 1.

Dude ... I just finished this, found the same solution ... EXCEPT, I included a "if not isdigit()" check into the return statement, because my dumb-ass though that the "moOse" example in the description had a zero instead of a capital 'o'... so I thought that we had to make sure that if a number is included, function returns False. Once I finished and saw your solution, I was looking at it for like solid 3 minutes, asking myself why is this here if it obviously doesn't fufill one of the requirements, before finally realizing that I confuzed 0 and O .... **** me.

no solution can be cleaner than mine

Wouldn't .casefold() be better used to check for both lower and upper?

this solution is doing unnecessary operation