a biker performs a trick in the air.
A biker is sitting still.
The biker cannot be sitting wile he performs a trick in the air.
exists e1 x1 x2 x3.(n_air(x3) & in(e1,x3) & Theme(e1,x2) & Actor(e1,x1) & v_perform(e1) & n_trick(x2) & n_biker(x1))
exists e1 s1 x1.(a_still(s1) & Manner(e1,s1) & Actor(e1,x1) & v_sit(e1) & n_biker(x1))