Two people singing on stage, one holding a guitar.
A guitarist and two singers are on stage.
Guitarists and singers are people.  One holding a guitar implies that they are a guitarist.
exists e1 e2 x1 x2 x3 x4 x5 x6.(a_topic(x1) & on(e1,x3) & rel(x3,x4) & Theme(e2,x6) & Actor(e2,x5) & v_hold(e2) & n_guitar(x6) & (x4 = x5) & n_thing(x4) & card_eq_1(x4) & n_stage(x3) & Actor(e1,x2) & v_sing(e1) & (x1 = x2) & n_people(x1) & card_eq_2(x1))
exists p1 x1 x2.(exists x3.(on(x1,x3) & n_stage(x3)) & n_singer(x1) & card_eq_2(x1) & of(x1,x2) & n_guitarist(x2))