“…Let u and x be two distinct white vertices of Q n and v and y be two distinct black vertices of Q n . It is proved in [8] that there are two disjoint paths P 1 and P 2 such that (1) P 1 is a path joining u to v, (2) P 2 is a path joining x to y, and (3) P 1 ∪ P 2 spans Q n . We call such property the be the 2P property.…”