([a-z]) (?!\1)([a-z]) (?!\1)(?!\2)([a-z]) (?!\1)(?!\2)(?!\3)([a-z]) (?!\1)(?!\2)(?!\3)(?!\4)([a-z]) (?!\1)(?!\2)(?!\3)(?!\4)(?!\5)([a-z]) (?!\1)(?!\2)(?!\3)(?!\4)(?!\5)(?!\6)([a-z]) (?!\1)(?!\2)(?!\3)(?!\4)(?!\5)(?!\6)(?!\7)([a-z]) (?!\1)(?!\2)(?!\3)(?!\4)(?!\5)(?!\6)(?!\7)(?!\8)([a-z])