A man uses a blowtorch on a test tube while students look on in the background.
The old white haired professor is using a blowtorch on a test tube.
A man using a blowtorch on a test tube in front of students can be anyone and need not be an old white haired professor.
exists e1 p1 x1 x2 x3 x4 x6.(n_background(x6) & exists e2 x5.(r_on(e2) & in(e2,x6) & Actor(e2,x5) & v_look(e2) & n_student(x5)) & while(e1,p1) & on(e1,x3) & n_tube(x3) & of(x3,x4) & n_test(x4) & Theme(e1,x2) & Actor(e1,x1) & v_use(e1) & n_blowtorch(x2) & n_man(x1))
exists e1 s1 s2 s3 x1 x2 x3 x4.(n_professor(x1) & a_haired(s3) & Theme(s3,x1) & a_white(s2) & Theme(s2,x1) & a_old(s1) & Theme(s1,x1) & Theme(e1,x2) & Actor(e1,x1) & v_use(e1) & on(x2,x3) & n_tube(x3) & of(x3,x4) & n_test(x4) & n_blowtorch(x2))