//#pragma GCC optimize("Ofast,no-stack-protector")
//#pragma GCC target("sse,sse2,sse3,ssse3,sse4,popcnt,abm,mmx,avx,avx2,tune=native")
#pragma GCC optimize("unroll-loops")
#pragma GCC optimize("Ofast")
/*#pragma GCC optimize("section-anchors")
#pragma GCC optimize("profile-values,profile-reorder-functions,tracer")
#pragma GCC optimize("vpt")
#pragma GCC optimize("rename-registers")
#pragma GCC optimize("move-loop-invariants")
#pragma GCC optimize("unswitch-loops")
#pragma GCC optimize("function-sections")
#pragma GCC optimize("data-sections")
#pragma GCC optimize("branch-target-load-optimize")
#pragma GCC optimize("branch-target-load-optimize2")
#pragma GCC optimize("btr-bb-exclusive")*/
//#pragma GCC optimize("inline")
#pragma comment(linker, "/STACK:167077260")
#define _CRT_SECURE_NO_WARNINGS
#include <chrono>
#include <set>
#include <map>
#include <deque>
#include <string>
#include <cstdint>
#include <cmath>
#include <queue>
#include <cassert>
#include <random>
#include <bitset>
#include <iomanip>
#include <numeric>
#include <time.h>//////////////
#include <ctime>
#include <climits>
#include <string>
#include <cstdio>
#include <vector>
#include <cstdlib>
#include <iostream>
#include <algorithm>
#include <unordered_map>
#include <unordered_set>
//++--++--++--++--++--++--++--++--++--++--++--++--++--++--++--++--++--++--++--++--++--++--++--++--++--++--++--++--++--++--++--++--++--++--++--++--++--++--++--++--++--++--++--++--++--++--++--++
//#define endl '\n'
#define mp make_pair
#define pbc push_back
#define pob pop_back()
#define empb emplace_back
#define queuel queue<long long>
#define sqr(a) ((a) * (a))
#define lsqr(a) (ld(a) * a)
#define all(x) (x).begin(), (x).end()
#define rall(x) (x).rbegin(), (x).rend()
#define pin(p) cin >> p.first >> p.second;
#define uniq(a) sort(all(a));(a).resize(unique(all(a)) - a.begin());
#define rev(v) reverse(v.begin(), v.end());
#define sout(s, c) for (auto i : s) cout << i << c;
#define pout(p) cout << p.first << " " << p.second;
#define er(v, l, r) erase(v.begin() + l, v.begin() + r);
#define vin(v) for (ll i = 0; i < v.size(); ++i) cin >> v[i];
#define vout(v, c) for (int i = 0; i < v.size(); ++i) cout << v[i] << c;
#define pushi(v, a) for (int i = 0; i < a.size(); ++i) v.push_back(a[i]);
#define fastio() ios_base::sync_with_stdio(0); cout.tie(0); cin.tie(0); srand(time(NULL))
#define dab(v) for(auto i:v)cout<<i<<' ';
#define sp system("pause")
#define left left228
#define type type1337
#define right right228
//++--++--++--++--++--++--++--++--++--++--++--++--++--++--++--++--++--++--++--++--++--++--++--++--++--++--++--++--++--++--++--++--++--++--++--++--++--++--++--++--++--++--++--++--++--++--++--++
using namespace std;
//++--++--++--++--++--++--++--++--++--++--++--++--++--++--++--++--++--++--++--++--++--++--++--++--++--++--++--++--++--++--++--++--++--++--++--++--++--++--++--++--++--++--++--++--++--++--++--++
typedef long long ll;
typedef long double ld;
typedef unsigned long long ull;
//++--++--++--++--++--++--++--++--++--++--++--++--++--++--++--++--++--++--++--++--++--++--++--++--++--++--++--++--++--++--++--++--++--++--++--++--++--++--++--++--++--++--++--++--++--++--++--++
const ld EPS = 1e-5;
const ld EPS2 = 1e-12;
const ld PI = acos(-1);
int mod = (int)998244353;
const int MOD7 = 1000000007;
const int MOD9 = 1000000009;
const int a228 = 18;
const int inf = 1e9;
//mt19937 rnd(time(0));
const ll kekmod = 1791791791;
const ll bestmod = 1148822869;
int n, m;
vector<vector<char>> a;

void check(vector<vector<char>> ta)
{
	vector<int> used(m);
	vector<vector<char>> rows;
	for (int j = 0; j < m; ++j)
	{
		vector<char> now;
		for (int i = 0; i < n; ++i)
		{
			now.pbc(ta[i][j]);
		}
		rows.pbc(now);
	}
	int bc = 0;
	for (int i = 0; i < m; ++i)
	{
		if (used[i])
		{
			continue;
		}
		bool f = 0;
		for (int j = 0; j < m; ++j)
		{
			if (used[j] || i == j) continue;
			rev(rows[j]);
			if (rows[j] == rows[i])
			{
				f = 1;
				used[i] = used[j] = 1;
				rev(rows[j]); break;
			}
			rev(rows[j]);
		}
		if (!f)
		{
			auto tr = rows[i];
			rev(tr);
			if (tr != rows[i]) return;
			bc++;
		}
	}
	if (bc == m % 2)
	{
		cout << "YES";
		sp;
		exit(0);
	}
}
vector<int> paira;
int npairid = -1;
void rec(int pos)
{
	if (pos == n)
	{
		auto tx = a;
		vector<int> keksd(n);
		int mv = 0;
		for (int j = 0; j < n; ++j)
		{
			if (!keksd[j] && j != npairid)
			{
				tx[mv] = a[j];
				tx[n - mv - 1] = a[paira[j]];
				keksd[j] = keksd[paira[j]] = 1;
				mv++;
			}
		}
		if (n % 2)
		{
			if (npairid == -1)return;
			tx[n / 2] = a[npairid];
		}
		check(tx);
		return;
	}
	if (paira[pos] != -1) rec(pos + 1);
	else
	{
		for (int j = pos + 1; j < n; ++j)
		{
			if (paira[j] == -1)
			{
				paira[j] = pos;
				paira[pos] = j;
				rec(pos + 1);
				paira[j] = paira[pos] = -1;
			}
		}
		if (n % 2)
		{
			if (npairid == -1)
			{
				npairid = pos;
				rec(pos + 1);
				npairid = -1;
			}
		}
	}
}
signed main()
{
	fastio();
	cin >> n >> m;
	a.resize(n, vector<char>(m));
	for (int i = 0; i < n; ++i) for (int j = 0; j < m; ++j) cin >> a[i][j];
	paira.resize(n, -1);
	rec(0);
	cout << "NO";
	sp;
}

Measured memory_bytes: 3132