A man in a T-shirt that says GNU is at the front of the room in front of a group of people sitting.
The class speaker lectures the students.
Not every class speaker is a man. Being at the front of the room doesn't mean you'll be giving lectures. Not all groups of people are students.
exists e1 p1 x1 x2 x3 x4 x6.(n_room(x6) & ne_org_gnu(x4) & a_topic(x1) & in(x1,x2) & exists p2 e2 x5 x7 x8 x9.(at(x4,x5) & of(x5,x6) & in(x6,x5) & of(x5,x7) & of(x7,x8) & Actor(e2,x9) & v_sit(e2) & (x8 = x9) & n_people(x8) & n_group(x7) & n_front(x5) & n_front(x5)) & Topic(e1,p1) & Actor(e1,x3) & v_say(e1) & (x2 = x3) & n_t-shirt(x2) & n_man(x1))
exists e1 x1 x2 x3.(n_student(x3) & n_speaker(x1) & of(x1,x2) & n_class(x2) & Theme(e1,x3) & Actor(e1,x1) & v_lecture(e1))