#include <bits/stdc++.h>
#define int long long
#define ll long long
using ull = unsigned long long;
using namespace std;
#define dump(x)                             \
    if (dbg) {                              \
        cerr << #x << " = " << (x) << endl; \
    }
#define overload4(_1, _2, _3, _4, name, ...) name
#define FOR1(n) for (ll i = 0; i < (n); ++i)
#define FOR2(i, n) for (ll i = 0; i < (n); ++i)
#define FOR3(i, a, b) for (ll i = (a); i < (b); ++i)
#define FOR4(i, a, b, c) for (ll i = (a); i < (b); i += (c))
#define FOR(...) overload4(__VA_ARGS__, FOR4, FOR3, FOR2, FOR1)(__VA_ARGS__)
#define FORR(i, a, b) for (int i = (a); i <= (b); ++i)
#define bit(n, k) ((n >> k) & 1) /*nのk bit目*/
namespace mydef {
const int INF = 1ll << 60;
const int MOD = 1e9 + 7;
template <class T>
bool chmin(T& a, const T& b) {
    if (a > b) {
        a = b;
        return 1;
    } else
        return 0;
}
template <class T>
bool chmax(T& a, const T& b) {
    if (a < b) {
        a = b;
        return 1;
    } else
        return 0;
}
void Yes(bool flag = true) {
    if (flag)
        cout << "Yes" << endl;
    else
        cout << "No" << endl;
}
void No(bool flag = true) {
    Yes(!flag);
}
void YES(bool flag = true) {
    if (flag)
        cout << "YES" << endl;
    else
        cout << "NO" << endl;
}
void NO(bool flag = true) {
    YES(!flag);
}
template <typename A, size_t N, typename T>
void Fill(A (&array)[N], const T& val) {
    std::fill((T*)array, (T*)(array + N), val);
}
bool dbg = false;
}  // namespace mydef
using namespace mydef;
#define pb push_back
#define mp make_pair
#define eb emplace_back
#define lb lower_bound
#define ub upper_bound
#define all(v) (v).begin(), (v).end()
#define SZ(x) ((int)(x).size())
#define vi vector<int>
#define vvi vector<vector<int>>
#define vp vector<pair<int, int>>
#define vvp vector<vector<pair<int, int>>>
#define pi pair<int, int>
//#define P pair<int, int>
//#define V vector<int>
//#define S set<int>
#define asn ans

int H, W;
string S[20];

bool f(const vi& v) {
    bool used[20] = {};
    int unused = 0;
    for (int i = 0; i < W; i++) {
        if (used[i])
            continue;
        for (int j = i + 1; j < W; j++) {
            if (used[i] || used[j])
                continue;
            //i,j列
            bool flag = 1;
            for (int k = 0; k < H; k++) {
                if (S[v[k]][i] != S[v[H - k - 1]][j]) {
                    flag = 0;
                    break;
                }
            }
            if (flag) {
                used[i] = 1;
                used[j] = 1;
                break;
            }
        }
        if (!used[i])
            unused++;
        if (W % 2 == 1 && unused >= 2)
            return false;
        if (W % 2 == 0 && unused >= 1)
            return false;
    }

    int n = -1;
    for (int i = 0; i < W; i++) {
        if (!used[i]) {
            n = i;
        }
    }
    if (n >= 0) {
        for (int i = 0; i < H; i++) {
            if (S[v[i]][n] != S[v[H - i - 1]][n])
                return false;
        }
    }

    return true;
}

void solve() {
    vi v(H, -1);
    for (int i = 0; i < (H + 1) / 2; i++) {
        v[i] = i;
    }
    sort(all(v));
    bool flag = false;
    do {
        vi w = v;
        int tmp = (H + 1) / 2;
        for (int i = 0; i < H; i++) {
            if (w[i] == -1)
                w[i] = tmp++;
        }
        vi V(H);
        for (int i = 0; i < H; i++) {
            V[w[i]] = i;
        }
        flag |= f(V);
    } while (next_permutation(all(v)));
    YES(flag);
}

signed main() {
    cin.tie(nullptr);
    ios::sync_with_stdio(false);
    cin >> H >> W;
    for (int i = 0; i < H; i++) {
        cin >> S[i];
    }
    solve();
    return 0;
}


Measured memory_bytes: 3596