#include <iostream>
#include <vector>
#include <algorithm>
#include <math.h>
#include <string>
#include <set>
#include <cstdio>
#include <iomanip>
#include <map>
#include <stdio.h>
#include <math.h>
#include <queue>
#include <random>
using namespace std;
#define IOS ios::sync_with_stdio(0); cin.tie(0); cout.tie(0)

int gcd(int a, int b) { return b ? a : gcd(b, a % b); }

int toNum(char s) {
	return s - 'a';
}

const int INF = 1e10;

//#pragma GCC optimize("Ofast")
//#pragma GCC target("sse,sse2,sse3,ssse3,sse4,popcnt,abm,mmx,avx,tune=native")

long long n,k,q,l,r;
double mi;
char kek;
string quest;
int a[100000];




bool isPalindrom(int left, int right) {
	if (left == right)
		return 1;
	if ((right - left) % 2 == 0) {
		while (right - left != 2) {
			if (a[left] != a[right])
				return 0;
			left++;
			right--;
		}
	}
	else {
		while (right - left != 1) {
			if (a[left] != a[right])
				return 0;
			left++;
			right--;
		}

	}
	return 1;
}

void change(int left, int right, int z) {
	for (int i = left; i <= right; i++)
		a[i] = z;
}

int main() {
	//freopen("sum.in", "r", stdin);
	//freopen("sum.out", "w", stdout);

	IOS;
	cin >> n >> q;
	for (int i = 0; i < n; i++) {
		cin >> kek;
		a[i] = toNum(kek);
	}
	for (int i = 0; i < q; i++) {
		cin >> quest;
		if (quest == "ask") {
			cin >> l >> r;
			if (isPalindrom(l - 1, r - 1))
				cout << "YES" << "\n";
			else
				cout << "NO" << "\n";
		}
		else {
			cin >> l >> r >> kek;
			change(l - 1, r - 1, toNum(kek));
		}
	}
	return 0;

}