A middle-aged man in a brown hat observes an open-air market.
A man is people watching at an open-air market.
The man is in an open-air market, where people congregate, and he observes the market, so we can infer that he is people watching.
exists e1 s1 s2 s3 x1 x2 x3.(Theme(e1,x3) & Actor(e1,x1) & v_observe(e1) & n_market(x3) & a_open-air(s3) & Theme(s3,x3) & in(x1,x2) & n_hat(x2) & a_brown(s2) & Theme(s2,x2) & n_man(x1) & a_middle-aged(s1) & Theme(s1,x1))
exists p1 x1.(exists e1 s1 x2 x3 x4.((x1 = x2) & at(e1,x4) & n_market(x4) & a_open-air(s1) & Theme(s1,x4) & Actor(e1,x3) & v_watch(e1) & (x2 = x3) & n_people(x2)) & n_man(x1))