The people were busy reading materials.
The people were busy typing up papers on the computer.
Reading and typing are two different activities.
exists e1 p1 x1.(n_people(x1) & exists e2 x2.(Theme(e2,x2) & Actor(e2,x1) & v_read(e2) & n_material(x2)) & Topic(e1,p1) & Actor(e1,x1) & v_busy(e1))
exists e1 p1 x1 x3.(n_computer(x3) & n_people(x1) & exists e2 s1 x2.(on(e2,x3) & a_up(s1) & Manner(e2,s1) & Theme(e2,x2) & Actor(e2,x1) & v_type(e2) & n_papers(x2)) & Topic(e1,p1) & Actor(e1,x1) & v_busy(e1))