6 :55 : bingo ! a-turn is IDd, we’re in Set C. n EE is BO,T1. N-1 EE was [BO,T1+BMrev] and the associated turn was a b one, in Set B. If considered n-1 EE was BO,T1, then in Set C with BO,T1 as new EE we’d have a-turn. That’s what is IDd here. If n-1 EE was BMrev, then we’d have c-turn as the...