#include <bits/stdc++.h>
#define ll long long
#define ull unsigned long long
#define fi first
#define se second

using namespace std;

const int mx = 1e5+10;
ll mod = 1e9+7;
ll p = 257;
ll P[mx];
ll prP[mx];

ull q = 263;
ull Q[mx];
ull prQ[mx];
void precalc(){
	prP[0] = prQ[0] = P[0] = Q[0] = 1;
	for(int i = 1; i < mx; i++){
		P[i] = (P[i-1]*p)%mod;
		Q[i] = Q[i-1]*q;
		prP[i] = (prP[i-1] + P[i])%mod;
		prQ[i] = prQ[i-1] + Q[i];
	}
}

pair<ll,ull> h[mx]; //on pref
pair<ll,ull> rh[mx]; //suf

void find_hashs(string s){
	int n = s.length();
	h[0].fi = 0;
	h[0].se = 0ull;
	for(int i = 1; i <= n; i++){
		h[i].fi = (h[i-1].fi*p + (ll)s[i-1])%mod;
		h[i].se = h[i-1].se*q + (ull)s[i-1];
	}

	rh[n].fi = 0;
	rh[n].se = 0ull;
	for(int i = n-1; i >= 0; i--){
		rh[i].fi = (rh[i+1].fi*p + (ll)s[i])%mod;
		rh[i].se = rh[i+1].se*q + (ull)s[i];
	}
}

pair<ll,ull> sub(int l, int r, bool go){
	if(go){
		pair<ll,ull> L = h[l];
		pair<ll,ull> R = h[r+1];
		L.fi = (L.fi*P[r-l+1])%mod;
		L.se = L.se*Q[r-l+1];
		return {((R.fi-L.fi)%mod+mod)%mod,R.se-L.se};
	}else{
		pair<ll,ull> L = rh[l];
		pair<ll,ull> R = rh[r+1];
		R.fi = R.fi*P[r-l+1]%mod;
		R.se = R.se*Q[r-l+1];
		return {((L.fi-R.fi)%mod+mod)%mod,L.se-R.se};
	}
}

pair< pair<ll,ull>,pair<ll,ull> > t[4*mx];
int psh[4*mx];

void build(int v, int tl, int tr){
	t[v] = {sub(tl,tr,1),sub(tl,tr,0)};
	if(tl==tr) return;
	int tm = (tl+tr)/2;
	build(v*2,tl,tm);
	build(v*2+1,tm+1,tr);
}

pair< pair<ll,ull>,pair<ll,ull> > combine(pair< pair<ll,ull>,pair<ll,ull> > L, pair< pair<ll,ull>,pair<ll,ull> > R, int szR, int szL){
	ll hsh1 = (L.fi.fi*P[szR] + R.fi.fi)%mod;
	ull hsh2 = (L.fi.se*Q[szR] + R.fi.se);
	ll rhsh1 = (L.se.fi + R.se.fi*P[szL])%mod;
	ull rhsh2 = (L.se.se + R.se.se*Q[szL]);
	return {{hsh1,hsh2},{rhsh1,rhsh2}};
}

void upd(int v, int tl, int tr, int val){
	if(val==0) return;
	t[v].fi = t[v].se = {(((ll)val)*prP[tr-tl])%mod,((ull)val)*prQ[tr-tl]};
}

void push(int v, int tl, int tr){
	if(psh[v]!=0){
		psh[v*2] = psh[v];
		psh[v*2+1] = psh[v];
		psh[v] = 0;
	}
	int tm = (tl+tr)/2;
	upd(v*2,tl,tm,psh[v*2]);
	upd(v*2+1,tm+1,tr,psh[v*2+1]);
}

pair< pair<ll,ull>,pair<ll,ull> > get(int v, int tl, int tr, int l, int r){
	if(tl==l && tr==r){
		return t[v];
	}
	push(v,tl,tr);
	int tm = (tl+tr)/2;
	if(l<=tm){
		if(r>=tm+1){
			auto L = get(v*2,tl,tm,l,tm);
			auto R = get(v*2+1,tm+1,tr,tm+1,r);
			int szR = r-(tm+1)+1;
			int szL = tm-l+1;
			return combine(L,R,szR,szL);
		}else{
			return get(v*2,tl,tm,l,r);
		}
	}else{
		return get(v*2+1,tm+1,tr,l,r);
	}
}

void upd(int v, int tl, int tr, int l, int r, int num){
	if(l>r) return;
	if(tl==l && tr==r){
		psh[v] = num;
		upd(v,tl,tr,num);
		return;
	}
	push(v,tl,tr);
	int tm = (tl+tr)/2;
	upd(v*2,tl,tm,l,min(tm,r),num);
	upd(v*2+1,tm+1,tr,max(tm+1,l),r,num);
	int szR = tr-tm;
	int szL = tm-tl+1;
	t[v] = combine(t[v*2],t[v*2+1],szR,szL);
}

main(){
	ios::sync_with_stdio(false);
	cin.tie(0);
	int n,q;
	string s;
	cin>>n>>q>>s;
	precalc();
	find_hashs(s);
	build(1,0,n-1);
	while(q--){
		string u;
		cin>>u;
		if(u[0]=='a'){
			int l,r;
			cin>>l>>r;
			l--;r--;
			auto t = get(1,0,n-1,l,r);
			if(t.fi==t.se){
				cout<<"YES"<<endl;
			}else{
				cout<<"NO"<<endl;
			}
		}else{
			int l,r;
			char c;
			cin>>l>>r>>c;
			l--;r--;
			upd(1,0,n-1,l,r,(int)c);
		}
	}
}