A person on a bmx bike.
A person walks alongside a BMX bike they are holding and propelling forward.
A person who walks alongside a bmx bike cannot be on a bmx bike
exists x1 x2 x3.(a_topic(x1) & on(x1,x2) & n_bike(x2) & of(x2,x3) & n_bmx(x3) & n_person(x1))
exists e2 e3 e1 s1 x1 x2 x3 x4 x5.(alongside(e1,x2) & a_forward(s1) & Manner(e3,s1) & Theme(e3,x5) & Actor(e3,x1) & v_propel(e3) & (x2 = x5) & n_thing(x1) & Theme(e2,x4) & Actor(e2,x1) & v_hold(e2) & (x2 = x4) & n_bike(x2) & (x2 = x3) & ne_org_bmx(x3) & Actor(e1,x1) & v_walk(e1) & n_person(x1))