The students are practicing martial arts.
The students are fighting
Martial arts is for fighting.
exists e1 s1 x1 x2.(n_student(x1) & Theme(e1,x2) & Actor(e1,x1) & v_practice(e1) & n_art(x2) & a_martial(s1) & Theme(s1,x2))
exists e1 x1.(n_student(x1) & Actor(e1,x1) & v_fight(e1))