A woman and a boy on a unicycle.
They're riding a bike
A unicycle has only one wheel while a bike has two wheels.
exists s1 x1 x2 x3.(a_topic(s1) & subset_of(x2,s1) & on(x2,x3) & n_unicycle(x3) & n_boy(x2) & subset_of(x1,s1) & n_woman(x1))
exists e1 x1 x2.(n_thing(x1) & Theme(e1,x2) & Actor(e1,x1) & v_ride(e1) & n_bike(x2))