There are several people in a park.
There is a group at the park.
A group consists of several people.
exists p1 x1 x2.(in(p1,x2) & n_park(x2) & exists s1 x3.((x1 = x3) & n_people(x3) & a_several(s1) & Theme(s1,x3)))
exists p1 x1 x3.(n_park(x3) & exists x2.((x1 = x2) & at(x2,x3) & n_group(x2)))