problem with sort

I'm not quite sure why this code doesn't works:

#include <iostream>
#include <algorithm>
#include <vector>
#include <string>
using namespace std;

class word
{
 string letters;
 string sorted;
 public:
 word(string&s)
 {
    letters=s;
    sort(s.begin(),s.end());
    sorted=s;
 }
 friend bool lt(word& a, word& b)
 {
   return (a.sorted < b.sorted) < 0 ? true: false;
 }
 friend ostream& operator<<(ostream& out, vector<word>& v)
 {
   for(int i=0; i<v.size(); ++i)
      cout << v[i].letters << endl;
   return out;
 }
};

int main()
{
  vector<word>dict;
  string aux;
  cin >> aux;

  while(aux!="#")
  {
     word w(aux);
     dict.push_back(w);

     cin >> aux;
  }

  sort(dict.begin(),dict.end(),lt);
  cout << dict << endl;

    return 0;
}

There's something wrong with the function "lt" but i'm not sure what.
In the prototype it says:
StrictWeakOrdering cmp but I'm not sure what does that mean, maybe
something about the kind of iterators I need to use?

Thanks!