Three men observe a specimen under a microscope.
Three scientists observe an experiment.
Men making microscope observations are not always scientists.  Microscope specimens are not always part of an experiment.
exists e1 x1 x2 x3.(under(e1,x3) & n_microscope(x3) & Theme(e1,x2) & Actor(e1,x1) & v_observe(e1) & n_specimen(x2) & n_man(x1) & card_eq_3(x1))
exists e1 x1 x2.(Theme(e1,x2) & Actor(e1,x1) & v_observe(e1) & n_experiment(x2) & n_scientist(x1) & card_eq_3(x1))