A big dog sniffs a little dog.
A big dog is sniffing.
dog sniffs is same as dog is sniffing
exists e1 s1 s2 x1 x2.(Theme(e1,x2) & Actor(e1,x1) & v_sniff(e1) & n_dog(x2) & a_little(s2) & Theme(s2,x2) & n_dog(x1) & a_big(s1) & Theme(s1,x1))
exists e1 s1 x1.(Actor(e1,x1) & v_sniff(e1) & n_dog(x1) & a_big(s1) & Theme(s1,x1))