A man sings on stage with a guitar.
A man is singing onstage.
WE DON'T KNOW THAT THE MAN IS SINGING.
exists e1 x1 x2 x3.(on(e1,x2) & with(x2,x3) & n_guitar(x3) & n_stage(x2) & Actor(e1,x1) & v_sing(e1) & n_man(x1))
exists e1 x1 x2.(Theme(e1,x2) & Actor(e1,x1) & v_sing(e1) & n_onstage(x2) & n_man(x1))