Someone is selling food on a set of doorsteps.
The doorsteps is where the person was selling food.
"Set of doorsteps" is a rephrasing of "doorsteps".
exists e1 x1 x2 x3 x4.(on(e1,x3) & of(x3,x4) & n_doorstep(x4) & n_set(x3) & Theme(e1,x2) & Actor(e1,x1) & v_sell(e1) & n_food(x2) & n_person(x1))
exists x1 x3.(n_person(x3) & n_doorstep(x1) & exists e2 e1 x2 x4.(n_location(x2) & Topic(e2,e1) & Actor(e2,x1) & v_be(e2) & loc_rel(e1,x2) & Theme(e1,x4) & Actor(e1,x3) & v_sell(e1) & n_food(x4)))