#define _USE_MATH_DEFINES
#include <bits/stdc++.h>
using namespace std;
// #define int long long
// #define double long double
#define rep(i,n) for (int i=0; i<(int)(n); ++i)
#define rep1(i,n) for (int i=1; i<(int)(n); ++i)
#define repeq(i,n) for (int i=0; i<=(int)(n); ++i)
#define rep1eq(i,n) for (int i=1; i<=(int)(n); ++i)
#define rrep(i,n) for (int i=(int)(n)-1; i>=0; --i)
#define rrep1(i,n) for (int i=(int)(n)-1; i>0; --i)
#define rrepeq(i,n) for (int i=(int)(n); i>=0; --i)
#define rrep1eq(i,n) for (int i=(int)(n); i>0; --i)
#define REP(i,a,b) for (int i=(int)(a); i<=(int)(b); ++i)
#define RREP(i,a,b) for (int i=(int)(a); i>=(int)(b); --i)
#define ALL(a) (a).begin(), (a).end()
#define RALL(a) (a).rbegin(), (a).rend()
using ll = long long;
using vi = vector<int>;
using vl = vector<ll>;
using vb = vector<bool>;
template<typename T> using Graph = vector<vector<T>>;
template<typename T> using Spacial = vector<vector<vector<T>>>;
using pii = pair<int, int>;
using pll = pair<ll, ll>;
const int MOD = 1e9+7;
const int MOD2 = 998244353;
// const double EPS = 1e-9;
const int dx[4] = {1, 0, -1, 0};
const int dy[4] = {0, 1, 0, -1};
string interval[2] = {" ", "\n"}; // {" ", "\n"}

template<typename T> struct is_plural : false_type{};
template<typename T1, typename T2> struct is_plural<pair<T1, T2>> : true_type{};
template<typename T> struct is_plural<vector<T>> : true_type{};
template<typename T> struct is_plural<complex<T>> : true_type{};
 
template<typename T1, typename T2> istream &operator>>(istream &is, pair<T1, T2> &p) { return is >> p.first >> p.second; }
template<typename T1, typename T2> ostream &operator<<(ostream &os, const pair<T1, T2> &p) { return os << p.first << " " << p.second; }
template<typename T> istream &operator>>(istream &is, vector<T> &vec) { for (auto itr = vec.begin(); itr != vec.end(); ++itr) is >> *itr; return is; }
template<typename T> ostream &operator<<(ostream &os, const vector<T> &vec) { if (vec.empty()) return os; bool pl = is_plural<T>(); os << vec.front(); for (auto itr = ++vec.begin(); itr != vec.end(); ++itr) os << interval[pl] << *itr; return os; }
 
bool CoutYN(bool a, string y = "Yes", string n = "No") { cout << (a ? y : n) << "\n"; return a; }

template<typename T1, typename T2> inline bool chmax(T1 &a, T2 b) { return a < b && (a = b, true); }
template<typename T1, typename T2> inline bool chmin(T1 &a, T2 b) { return a > b && (a = b, true); }

int modpow(int a, long long n, int mod = MOD) { int ret = 1; do { if (n & 1) ret = 1LL * ret * a % mod; a = 1LL * a * a % mod; } while (n >>= 1); return ret; }

template<typename T1, typename T2> bool CompareBySecond(pair<T1, T2> a, pair<T1, T2> b) { return a.second != b.second ? a.second < b.second : a.first < b.first; }
// counterclockwise from 12 o'clock direction
template<typename T> bool CompareBySlope(pair<T, T> a, pair<T, T> b) { if (a.first * b.first < 0) return a.first < b.first; if (a.first == 0) return a.second >= 0 || b.first > 0; if (b.first == 0) return b.second < 0 && a.first < 0; return a.second * b.first < a.first * b.second; }


/* -------- <templates end> -------- */


typedef pair<char, char> pcc;
Graph<char> g(12, vector<char>(12));
vector<pii> pairs;
bitset<12> rest;

bool dfs(Spacial<int> &det, Graph<bool> &bdet, int alone) {
  if (rest.none()) {
    int w = det[0][0].size();
    vi arr(w, (1<<w)-1);
    for (auto &p : pairs) {
      if (!bdet[p.first][p.second]) return false;
      rep(i,w) {
        arr[i] &= det[p.first][p.second][i];
      }
    }
    if (alone != -1) {
      if (!bdet[alone][alone]) return false;
      rep(i,w) {
        arr[i] &= det[alone][alone][i];
      }
    }
    rep(i,w) {
      if (!arr[i]) return false;
    }
    return true;
  }

  int idx = 0;
  while (!rest[idx]) ++idx;
  rest[idx] = false;
  REP(i,idx+1,11) {
    if (rest[i]) {
      pairs.emplace_back(idx, i);
      rest[i] = false;
      if (dfs(det, bdet, alone)) return true;
      rest[i] = true;
      pairs.pop_back();
    }
  }
  rest[idx] = true;
  return false;
}

bool row(int h, int w) {
  Spacial<int> det(h, Graph<int>(h, vi(w, 0)));
  Graph<bool> bdet(h, vb(h, true));

  rep(i,h) {
    map<char, int> self;
    rep(k,w) {
      self[g[i][k]] += 1<<k;
    }
    bool odd = false;
    for (auto &p : self) {
      bitset<12> s(p.second);
      if (s.count() & 1) {
        if (odd) {
          bdet[i][i] = false;
          break;
        }
        odd = true;
      }
      rep(k,w) {
        if (s[k]) {
          det[i][i][k] = p.second;
        }
      }
    }

    rep(j,i) {
      map<pcc, int> comb;
      rep(k,w) {
        comb[{g[i][k], g[j][k]}] += 1<<k;
      }
      bool odd = false;
      for (auto &p : comb) {
        pcc q = {p.first.second, p.first.first};
        bitset<12> s(p.second);
        if (!comb.count(q)) {
          bdet[i][j] = bdet[j][i] = false;
          break;
        }
        if (q.first == q.second) {
          if (s.count() & 1) {
            if (odd) {
              bdet[i][j] = bdet[j][i] = false;
              break;
            }
            odd = true;
          }
        } else if (__builtin_popcount(comb[q]) != s.count()) {
          bdet[i][j] = bdet[j][i] = false;
          break;
        }
        rep(k,w) {
          if (s[k]) {
            det[i][j][k] = det[j][i][k] = comb[q];
          }
        }
      }
    }
  }

  rest = (1<<h)-1;
  if (h&1) {
    rep(i,h) {
      rest[i] = false;
      if (dfs(det, bdet, i)) return true;
      rest[i] = true;
    }
    return false;
  }
  return dfs(det, bdet, -1);
}

void solve() {
  int h, w; cin >> h >> w;
  rep(i,h) rep(j,w) cin >> g[i][j];

  CoutYN(row(h, w), "YES", "NO");
}


/* -------- <programs end> -------- */


signed main() {
  cin.tie(nullptr);
  ios::sync_with_stdio(false);
  cout << fixed << setprecision(12);
  solve();
  return 0;
}


Measured memory_bytes: 256