Karate students practicing on a mat.
The students are all boys.
Not all Karate students are boys.
exists e1 x1 x2 x3 x4.(a_topic(x1) & on(e1,x4) & n_mat(x4) & Actor(e1,x3) & v_practice(e1) & (x1 = x3) & n_student(x1) & (x1 = x2) & ne_nam_karate(x2))
exists p1 x1.(n_student(x1) & all x2.(n_boy(x2) -> (x1 = x2)))