A man sitting on the back of a truck underneath an umbrella.
A man is sitting outside in the rain.
There is no mention of the location of the truck or the weather so one cannot assume it is located outside nor can one assume it is raining.
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 p1 x1 x2.(n_rain(x2) & in(e1,x2) & exists s1.(Theme(s1,x1) & a_outside(s1)) & Topic(e1,p1) & Actor(e1,x1) & v_sit(e1) & n_man(x1))