premise: A girl is standing and another one is sitting by a tree
hypothesis: Both girls are sitting by the tree.
explanation_1: The girls cannot simultaneously both be sitting and one is standing and one sitting.
explanation_2: One one girl is sitting, the other is standing.  Therefore we cannot say that both are sitting since there is at least one that is standing.
explanation_3: If a girl is standing then both girls cannot be sitting.
premise_logic: exists e1 e2 x1 x2 x3.(by(e2,x3) & n_tree(x3) & Actor(e2,x2) & v_sit(e2) & n_thing(x2) & card_eq_1(x2) & -(x2 = x1) & n_thing(x1) & card_eq_1(x1) & Actor(e1,x1) & v_stand(e1) & n_girl(x1))
hypothesis_logic: exists e1 x1 x2.(n_tree(x2) & n_girl(x1) & by(e1,x2) & Actor(e1,x1) & v_sit(e1))