Three workers are performing their jobs while on scaffolding.
Some humans performing
Workers are likely to be humans, although they could be extra-terrestrials, animal workers, etc.  The fact that they were on scaffolding means that the workers are likely human.  In both cases they are performing.
exists e1 x1 x2 x3.(on(e1,x3) & n_scaffolding(x3) & r_while(e1) & Theme(e1,x2) & Actor(e1,x1) & v_perform(e1) & n_job(x2) & of(x2,x1) & n_thing(x1) & n_worker(x1) & card_eq_3(x1))
exists e1 x1 x2.(a_topic(x1) & Actor(e1,x2) & v_perform(e1) & (x1 = x2) & n_human(x1))