#if __has_include("../library/Basic/Debug.hpp")

#include "../library/Basic/Debug.hpp"

#else

/* ----- Header Files ----- */
// IO
#include <cstdio>
#include <iomanip>
#include <ios>
#include <iostream>

// algorithm
#include <algorithm>
#include <cmath>
#include <numeric>

// container
#include <vector>
#include <string>
#include <tuple>
#include <complex>
#include <set>
#include <map>
#include <stack>
#include <queue>
#include <deque>
#include <bitset>

// others
#include <random>
#include <limits>
#include <functional>
#include <ctime>
#include <cassert>
#include <cstdint>


/* ----- Type Alias ----- */
using Bool = bool;
using Int = long long int;
using Real = long double;
using Char = char;
using String = std::string;
template <class T, class U>
using Pair = std::pair<T, U>;
template <class... Ts>
using Tuple = std::tuple<Ts...>;

template <class T>
using Vector = std::vector<T>;
template <size_t N>
using Bits = std::bitset<N>;
template <class T>
using Queue = std::queue<T>;
template <class T>
using Stack = std::stack<T>;
template <class T>
using Deque = std::deque<T>;

template <class T>
using MaxHeap = std::priority_queue<T>;
template <class T>
using MinHeap = std::priority_queue<T, std::vector<T>, std::greater<T>>;
template <class T>
using Set = std::set<T>;
template <class T, class U>
using Map = std::map<T, U>;

template <class T, class... Us>
using Func = std::function<T(Us...)>;

template <class T>
T genv(T v) { return v; }

template <class T, class... Ts>
auto genv(size_t l, Ts... ts) {
    return Vector<decltype(genv<T>(ts...))>(l, genv<T>(ts...));
}

template <class Cost = Int>
struct Edge {
    Int src, dst;
    Cost cost;
    Edge(Int src = -1, Int dst = -1, Cost cost = 1)
        : src(src), dst(dst), cost(cost){};

    bool operator<(const Edge<Cost>& e) const { return this->cost < e.cost; }
    bool operator>(const Edge<Cost>& e) const { return this->cost > e.cost; }
};

template <class Cost = Int>
using Edges = Vector<Edge<Cost>>;
template <class Cost = Int>
using Graph = Vector<Vector<Edge<Cost>>>;

#endif

/* ----- Misc ----- */
void fastio() {
    std::ios::sync_with_stdio(false);
    std::cin.tie(nullptr);
}

struct Fout {
    Int precision;
    Fout(Int precision) : precision(precision) {}
};
std::ostream& operator<<(std::ostream& os, const Fout& fio) {
    os << std::fixed << std::setprecision(fio.precision);
    return os;
}


/* ----- Constants ----- */
// constexpr Int INF = std::numeric_limits<Int>::max() / 3;
// constexpr Int MOD = 1000000007;
// constexpr Real PI = acos(-1);
// constexpr Real EPS = 1e-10;
// std::mt19937 mt(int(std::time(nullptr)));

struct {
    Int h, w;
    Vector<String> s, t;
    Bool possible;
    Vector<Int> col;

    void check(Int b) {
        Int x;
        for (x = 0; x < w; ++x) {
            if (!((b >> x) & 1)) break;
        }

        if (x == w) {
            std::cout << "YES" << std::endl;
            std::exit(0);
        }

        String z = t[x];
        std::reverse(z.begin(), z.end());

        for (Int y = x + 1; y < w; ++y) {
            if (!((b >> y) & 1)) {
                if (t[y] == z) {
                    check(b | (1 << x) | (1 << y));
                }
            }
        }
    }

    void check_lonely() {
        if (w % 2 == 0) {
            check(0);
        } else {
            for (Int x = 0; x < w; ++x) {
                String z = t[x];
                std::reverse(z.begin(), z.end());
                if (z == t[x]) check(1 << x);
            }
        }
    }

    void align() {
        for (Int y = 0; y < w; ++y) {
            for (Int x = 0; x < h; ++x) {
                t[y][x] = s[col[x]][y];
            }
        }
        check_lonely();
    }

    void enumcol(Int b, Int i) {
        Int x;
        for (x = 0; x < h; ++x) {
            if (!((b >> x) & 1)) break;
        }
        if (x == h) {
            align();
            return;
        }

        for (Int y = x + 1; y < h; ++y) {
            if (!((b >> y) & 1)) {
                col[i] = x;
                col[h - i - 1] = y;
                enumcol(b | (1 << x) | (1 << y), i + 1);
            }
        }
    }

    void enumcol_lonely() {
        if (h % 2 == 0) {
            enumcol(0, 0);
        } else {
            for (Int x = 0; x < h; ++x) {
                col[h / 2] = x;
                enumcol(1 << x, 0);
            }
        }
    }

    void operator()() {
        possible = false;
        std::cin >> h >> w;

        s.resize(h), t.resize(w);
        for (auto& x : s) std::cin >> x;
        for (auto& y : t) y.resize(h);

        col.resize(h);
        enumcol_lonely();
    }
} solve;

int main() {
    solve();
    std::cout << "NO" << std::endl;
    return 0;
}


Measured memory_bytes: 256