People are sitting at desks in a library.
People are spending their time at the library
People spending time at the library means the same thing as people in a library.
exists e1 x1 x2 x3.(in(e1,x3) & n_library(x3) & at(e1,x2) & n_desk(x2) & Actor(e1,x1) & v_sit(e1) & n_people(x1))
exists e1 x1 x2 x3.(n_library(x3) & at(e1,x3) & Theme(e1,x2) & Actor(e1,x1) & v_spend(e1) & n_time(x2) & of(x2,x1) & n_thing(x1) & n_people(x1))