Agreed. He removed the second B2B2 probability annotation as though it were a repeat of the first and inapplicable to the probability set, but that's not the case, and it shouldn't be removed. Apply lower-case to the younger boy in the probability sets and it's clear why. B2b2 is not the same occurrence as b2B2. Even though the day both were born on was "a Tuesday" doesn't mean both probability instances are referring to the exact same event. Except in the case of twins, which is outside the scope of the exercise.