#include <bits/stdc++.h>
using namespace std;
int main(){
long long k ;cin >> k;
long long m = 0;
string s[100001];
do{
stack <long long> b;
queue <long long> a;
long long tmp;
cin >> tmp ;
if(tmp==1) a.push(tmp);
else{ b.push(tmp);a.push(0);}
for(int i = 2 ; i <= k ; i++){
cin >> tmp ;
if( tmp == a.back() + 1 ){
a.push(tmp);
while( b.size()!=0 && b.top() == a.back()+1){
a.push(b.top());
b.pop();
}}
else b.push(tmp);
}
if(a.front()==0) a.pop();
s[m]="yes";
if(b.size()!=0){
if(b.top() == a.back()+1){
while(b.size()!=1){
tmp = b.top();
b.pop();
if(tmp!=b.top()-1){
s[m]="no";
}
}}
else s[m]="no";
}
m++;
cin >> k;
}while(k!=0);
for(int i = 0 ; i <=m-2 ; i++ ) cout << s[i]<< "\n";
cout << s[m-1];
return 0;
}
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