premise: Very large group of old people riding in boats down a river.
hypothesis: Mob of elderly riding water crafts.
explanation_1: Old people and elderly mean the same thing. A boat is a water craft.
explanation_2: A large group could be called a mob.
explanation_3: Very large group of old people are a mob of elderly, and boats are water crafts.
premise_logic: exists e1 s1 s2 x1 x2 x3 x4 x5 x6.(a_topic(x1) & of(x1,x3) & down(e1,x6) & n_river(x6) & in(e1,x5) & n_boat(x5) & Actor(e1,x4) & v_ride(e1) & (x3 = x4) & n_people(x3) & a_old(s2) & Theme(s2,x3) & n_group(x1) & a_large(s1) & Theme(s1,x1) & (x1 = x2) & ne_nam_very(x2))
hypothesis_logic: exists s1 s2 x1 x2 x3.(ne_nam_mob(s1) & a_topic(s1) & of(s1,x1) & n_craft(x1) & of(x1,x3) & n_water(x3) & of(x1,x2) & n_riding(x2) & a_elderly(s2) & Theme(s2,x1))