A class full of students.
There is a teacher at the front of the classroom
we don't know there is a teacher in front of the classroom.
exists s1 x1 x2 x3.(a_topic(x1) & of(s1,x3) & n_student(x3) & Theme(s1,x2) & a_full(s1) & (x1 = x2) & n_class(x1))
exists p1 x1 x3 x4.(n_classroom(x4) & n_front(x3) & exists x2.((x1 = x2) & at(x2,x3) & of(x3,x4) & n_teacher(x2)))