“…• p 1 pointing in T n towards the root r(T n ), with L 1 =R n , • p 2 pointing in S n towards the root r(S n ), with L 2 =B n , • p 3 pointing inT n towards the root r(T n+1 ), with L 3 = {r(T n+1 ), y}, • p 4 pointing inS n towards the root r(S n+1 ), with L 4 = {r(S n+1 ), g}. (6) Note that our construction so far has been tailored to provide us with a P -respecting isomorphism…”