A choir performing for an audience.
The choir is singing.
A choir performs by singing.
exists e1 x1 x2 x3.(a_topic(x1) & for(e1,x3) & n_audience(x3) & Actor(e1,x2) & v_perform(e1) & (x1 = x2) & n_choir(x1))
exists e1 x1.(n_choir(x1) & Actor(e1,x1) & v_sing(e1))