A small child is riding on a toboggan.
The small child is riding a bicycle.
A child cannot be riding a toboggan and a bicycle at the same time.
exists e1 s1 x1 x2.(on(e1,x2) & n_toboggan(x2) & Actor(e1,x1) & v_ride(e1) & n_child(x1) & a_small(s1) & Theme(s1,x1))
exists e1 s1 x1 x2.(n_child(x1) & a_small(s1) & Theme(s1,x1) & Theme(e1,x2) & Actor(e1,x1) & v_ride(e1) & n_bicycle(x2))