Isogram function implementation

bool FBullCowGame::IsIsogram(FString Word) const
{
	//Treat 0-1 letter strings as isograms
	if (Word.length() <= 1) { return true; }
	//setup our map
	TMap <char, bool> LetterSeen;
	//Loop through the letters of the word
	for (auto Letter : Word) 
	{
		Letter = tolower(Letter);
		//if the letter is in the map
		if (LetterSeen[Letter]) 
		{
			return false;//it is not an isogram
		}
		else //otherwise
		{
			LetterSeen[Letter] = true;//add the letter to the map
		}
	}
		

	return true;//for example of cases of /0
}