T1:=C<O; T2:=REF(T1,1) AND T1 AND V>REF(V,1); T3:=REF(T2,1) AND T1 AND V<REF(V,1); T4:=REF(T3,1) AND T1 AND V<REF(V,1); XG:REF(T4,1) AND C>O AND V>REF(V,1);