Not quite. You do not need brackets around the character sets with tr. If you put brackets around in both cases, then you're just adding two characters (mapped to themselves) in the transliteration list, at best, and (if the left bracket is already in the list, mapped to something other than the left bracket) possibly breaking the transliteration, at worst. You're right about the space not being needed, though in this particular case it doesn't do any harm.