A group of girls in leotards.
Some ballerinas are practicing.
Just because A group of girls in leotards doesn't mean they are ballerinas.
exists x1 x2 x3.(a_topic(x1) & of(x1,x2) & in(x2,x3) & n_leotard(x3) & n_girl(x2) & n_group(x1))
exists e1 x1.(Actor(e1,x1) & v_practice(e1) & n_ballerina(x1))