With no explanation, label text_A→text_B with either "not_related" or "related".
text_A: Russ raps.
text_B: Roger Federer was the defending champion , but lost to Juan Martin del Potro 6 -- 4 , 6 -- 7 -LRB- 5 -- 7 -RRB- , 7 -- 6 -LRB- 7 -- 3 -RRB- in the final .. Juan Martin del Potro. Juan Martin del Potro. Roger Federer. Roger Federer
not_related.