Usain Bolt is in the lead of a race in the 2012 London Olympics.
Usain Bolt fell behind the pack in the race.
If Usain Bolt is in the lead he did not fall behind the pack of a race.
exists p1 x1 x2 x3 x5 x6.(ne_geo_olympics(x5) & (x5 = x6) & ne_geo_london(x6) & n_date(x5) & a_date_year_2012(x5) & a_date_year_2012(x5) & n_lead(x3) & ne_org_bolt(x1) & (x1 = x2) & ne_org_usain(x2) & exists x4.(in(x1,x3) & of(x3,x4) & in(x4,x5) & n_race(x4)))
exists e1 x1 x2 x3 x4.(n_race(x4) & n_pack(x3) & ne_org_bolt(x1) & (x1 = x2) & ne_org_usain(x2) & behind(e1,x3) & in(x3,x4) & Actor(e1,x1) & v_fall(e1))