Someone on a Nitro snowboard in midair and another person on the ground behind them.
Someone is on a Nitro snowboard.
Someone on and someone is on are synonymous.
exists s1 x1 x2 x3 x4 x5 x6.(n_ground(x6) & a_topic(s1) & subset_of(x5,s1) & on(x5,x6) & behind(x6,x1) & n_thing(x1) & n_person(x5) & -(x5 = x1) & n_person(x1) & subset_of(x1,s1) & on(x1,x2) & in(x2,x4) & n_midair(x4) & n_snowboard(x2) & (x2 = x3) & ne_org_nitro(x3) & n_person(x1))
exists p1 x1.(exists x2 x3.(on(x1,x2) & n_snowboard(x2) & (x2 = x3) & ne_org_nitro(x3)) & n_person(x1))