$RP^{[d]}$ is an equivalence relation: An enveloping semigroup proof
  We present a purely enveloping semigroup proof of a theorem of Shao and Ye which asserts that for an abelian group $T$, a minimal flow $(X,T)$ and any integer $d \ge 1$, the regional proximal relation of order $d$ is an equivalence relation. 
Eli Glasner
math.DS