A man sitting on the back of a truck underneath an umbrella.
The man's son holds an umbrella for his father
Only one man is mentioned in sentence one and therefore no relationship of father and son can be deduced.
exists e1 x1 x2 x3 x4 x5.(n_back(x3) & a_topic(x1) & on(e1,x3) & of(x3,x4) & underneath(x4,x5) & n_umbrella(x5) & n_truck(x4) & Actor(e1,x2) & v_sit(e1) & (x1 = x2) & n_man(x1))
exists e1 x1 x2 x3 x4.(n_father(x4) & of(x4,x1) & n_male(x1) & n_son(x2) & of(x2,x1) & n_man(x1) & for(e1,x4) & Theme(e1,x3) & Actor(e1,x2) & v_hold(e1) & n_umbrella(x3))