Rene Villarreal: This is a bit of nitpicking, but I think C18C17B17C19A17B18 is a superior refutation against C18 (compared to the current variation) since it loses 2 stones instead of 3 for life.
Sadaharu: Your moves have been added. Actually it's the same since taking 2 stones is sente while taking 3 stones is gote.
@Sadaharu you are right! I didn't think of the sente when making my comment