My IsIsogram() solution

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bool FBullCowGame::IsIsogram(FString Word) const
{
	TMap<char, bool> LetterSeen;

	for (auto Letter : Word) {
		Letter = tolower(Letter);
		if (LetterSeen[Letter] != true) {
			LetterSeen[Letter] = true;
		}
		else {
			// we have seen the letter before, so the word is no isogram
			return false;
		}
	}
	// no letter was seen before, so every letter is unique => isogram
	return true;
}