a snowboarder wearing red is descending a snow covered mountain.
the swimmer swam alone
Two different different people are mentioned, a snowboarder and a swimmer.  Also the sentences mention them doing two different things, swimming and descending a mountain.
exists e3 e2 e1 x1 x2 x3 x4.(Theme(e3,x3) & Actor(e3,x1) & v_descend(e3) & n_mountain(x3) & Theme(e2,x3) & v_cover(e2) & of(x3,x4) & n_snow(x4) & n_red(x1) & Actor(e1,x1) & v_wear(e1) & of(x1,x2) & n_snowboarder(x2))
exists x1 x2.(n_swam(x1) & of(x1,x2) & n_swimmer(x2) & a_topic(x1) & r_alone(x1))