Someone riding sideways on a motorcycle.
There is a person on a machine.
The machine could refer to a motorcycle since a motorcycle is a type of machine.
exists e1 x1 x2.(on(e1,x2) & n_motorcycle(x2) & Actor(e1,x1) & v_sideway(e1) & n_riding(x1))
exists p1 x1 x2 x3.((x1 = x2) & on(x2,x3) & n_machine(x3) & n_person(x2))