//#include <bits/stdc++.h>

#include <iostream>
#include <algorithm>

#include <bitset>
#include <vector>
#include <set>
#include <map>
#include <unordered_set>
#include <unordered_map>
#include <stack>
#include <queue>
#include <deque>
#include <cstring>
#include <string>
#include <utility>
#include <array>
#include <complex>
#include <valarray>

#include <cassert>
#include <cmath>
#include <functional>
#include <iomanip>
#include <chrono>
#include <random>
#include <numeric>


using namespace std;
#define int long long

typedef long long ll;
typedef unsigned long long ull;
//typedef unsigned __int128 HASH;
typedef pair<int,int> pii;
typedef pair<ll, ll> pll;
typedef pair<ull, ull> pullull;
typedef pair<ll,int> plli;
typedef pair<long double, int> pdbi;
typedef pair<int,pii> pipii;
typedef pair<ll,pll> plpll;
typedef vector<int> vi;
typedef vector<ll> vll;
typedef vector<vi> vvi;
typedef vector<vvi> vvvi;
typedef vector<pii> vpii;
typedef vector<vector<int>> mat;

#define rep(i,n) for (int i=0;i<(n);i++)
#define rep2(i,a,b) for (int i=(a);i<(b);i++)
#define rrep(i,n) for (int i=(n);i>0;i--)
#define rrep2(i,a,b) for (int i=(a);i>b;i--)
#define pb push_back
#define fi first
#define se second
#define all(a) (a).begin(),(a).end()
#define rall(a) (a).rbegin(),(a).rend()

const ll hmod1 = 999999937;
const ll hmod2 = 1000000000 + 9;
const int INF = 1<<30;
const ll INFLL = 1LL<<62;
const long double EPS = 1e-12;
const ll mod = 1000000000 + 7;
const int dx4[4] = {1, 0, -1, 0};
const int dy4[4] = {0, 1, 0, -1};
const int dx8[8] = {1, 1, 1, 0, 0, -1, -1, -1};
const int dy8[8] = {0, 1, -1, 1, -1, 0, 1, -1};
const long double pi = 3.141592653589793;

#define addm(X, Y) (X) = ((X) + ((Y) % mod) + mod) % mod
#define inside(y, x, h, w) (0 <= (y) && (y) < (h) && 0 <= (x) && (x) < (w)) ? true : false

//debug
#define DEBUG

#define DUMPOUT cout

#ifdef DEBUG
#define dump(...) DUMPOUT<<#__VA_ARGS__<<" :["<<__FUNCTION__<<":"<<__LINE__<<"]"<<endl; DUMPOUT<<"    "; dump_func(__VA_ARGS__)
#else
#define dump(...)
#endif

void dump_func() {DUMPOUT << endl;};

template <class Head, class... Tail> void dump_func(Head&& head, Tail&&... tail) {
    DUMPOUT << head;
    if (sizeof...(Tail) == 0) DUMPOUT << " ";
    else DUMPOUT << ", ";
    dump_func(std::move(tail)...);
}

//ostream
template<typename T> ostream& operator << (ostream& os, vector<T>& vec) {
    os << "["; for (int i = 0; i<vec.size(); i++) os << vec[i] << (i + 1 == vec.size() ? "" : ", "); os << "]";
    return os;
}

template<typename T, typename U> ostream& operator << (ostream& os, pair<T, U>& pair_var) {
    os << "(" << pair_var.first << ", " << pair_var.second << ")";
    return os;
}

template<typename T, typename U> ostream& operator << (ostream& os, map<T, U>& map_var) {
    os << "[";
    for (auto itr = map_var.begin(); itr != map_var.end(); itr++) {
        os << "(" << itr->first << ", " << itr->second << ")"; itr++;  if(itr != map_var.end()) os << ", "; itr--;
    }
    os << "]";
    return os;
}

template<typename T> ostream& operator << (ostream& os, set<T>& set_var) {
    os << "[";
    for (auto itr = set_var.begin(); itr != set_var.end(); itr++) {
        os << *itr; ++itr; if(itr != set_var.end()) os << ", "; itr--;
    }
    os << "]";
    return os;
}

int h, w;
//char c[12][12];
vector<string> s;
vector<pii> ps;
bool used[12];

signed main(){
  cin.tie(0);
  ios::sync_with_stdio(false);
  cin >> h >> w;
  rep(i, h) {
    string tmp;
    cin >> tmp;
    s.push_back(tmp);
  }
  vector<string> ss = s;
  rep(i, h) sort(all(ss[i]));
  rep(i, h) {
    if (used[i]) continue;
    rep2(j, i + 1, h) {
      if (used[j]) continue;
      if (ss[i] == ss[j]) {
        //cout << i << " " << j << endl;
        used[i] = true;
        used[j] = true;
        ps.push_back({i, j});
        break;
      }
    }
  }
  int cnt = 0;
  rep(i, h) {
    if (!used[i]) cnt++;
  }
  if (cnt >= 2 || (cnt == 1 && h % 2 == 0)) {
    cout << "NO" << endl;
    return 0;
  }
  //cout << cnt << endl;
  rep(i, ps.size()) {
    rep(j, w) used[j] = false;
    pii p = ps[i];
    rep(j, w) {
      if (used[j]) continue;
      //cout << j << endl;
      rep2(k, j + 1, w) {
        //cout << j << endl;
        if (used[k]) continue;
        if (s[p.fi][j] == s[p.se][k] && s[p.se][j] == s[p.fi][k]) {
          //cout << s[p.fi][j] << " " << s[p.se][k] << endl;
          //cout << s[p.se][j] << " " << s[p.fi][k] << endl;
          //cout << j << " " << k << endl;
          used[j] = true;
          used[k] = true;
          break;
        }
      }
    }
    cnt = 0;
    rep(k, w) {
      if (!used[k]) {
        //cout << k << endl;
        cnt++;
      }
    }
    //cout << "---------------" << endl;
    /*
    cout << cnt << endl;
    cout << s[p.fi] << endl;
    cout << s[p.se] << endl;
    */
    if (cnt >= 2 || (cnt == 1 && w % 2 == 0)) {
      cout << "NO" << endl;
      return 0;
    }
  }
  cout << "YES" << endl;
}


Measured memory_bytes: 256