The baby sits on the sandy beach.
A baby is sitting beachside.
Sitting beachside is a rephrasing of sits on the sandy beach.
exists e1 x1 x2 x3.(n_beach(x2) & of(x2,x3) & n_sandy(x3) & n_baby(x1) & on(e1,x2) & Actor(e1,x1) & v_sit(e1))
exists p1 x1.(exists e1 x2.((x1 = x2) & n_beachside(x2) & Actor(e1,x2) & v_sit(e1)) & n_baby(x1))