sd(u,v)={
  my(r=List());
  u=vecsort(u,,8);
  v=vecsort(v,,8);
  for(i=1,#u,if(!setsearch(v,u[i]),listput(r,u[i])));
  for(i=1,#v,if(!setsearch(u,v[i]),listput(r,v[i])));
  Vec(r)
};
sd(["John", "Serena", "Bob", "Mary", "Serena"],["Jim", "Mary", "John", "Jim", "Bob"])