Dark-haired art student working on a project while standing up.
Student sitting down, writing an essay.
A student can't be sitting down and standing up at the same time.  A project is not the same as an essay.
exists e2 e1 s1 s2 x1 x2 x3 x4.(a_topic(x1) & while(e1,e2) & a_up(s2) & Manner(e2,s2) & Actor(e2,x3) & v_stand(e2) & on(e1,x4) & n_project(x4) & Actor(e1,x3) & v_work(e1) & (x1 = x3) & n_student(x1) & of(x1,x2) & n_art(x2) & a_dark-haired(s1) & Theme(s1,x1))
exists e2 e1 s1 x1 x2 x3.(Theme(e2,x3) & Actor(e2,x2) & v_write(e2) & n_essay(x3) & n_student(x2) & a_down(s1) & Manner(e1,s1) & Actor(e1,x1) & v_sit(e1) & n_student(x1))