People at a kickboxing class.
They are kickboxing
The people will be kickboxing at the class, because that's what the class is about.
exists e1 x1 x2.(a_topic(x1) & at(x1,x2) & n_class(x2) & Actor(e1,x2) & v_kickbox(e1) & n_people(x1))
exists e1 x1.(n_thing(x1) & Actor(e1,x1) & v_kickbox(e1))