#include <bits/stdc++.h>

using namespace std;

int main()
{

    int x;

    while(1)
    {
        int ok=0;
        scanf("%d", &x);
        if(x==0) break;
        for(int i=1; i<=x; i++)
        {

            int k;
            scanf("%d", &k);
            int m=1;
            stack<int>pilha;
            if(k==m)
            {
                m++;
                ok=1;
            }
            else if(k!=m)
            {
                pilha.push(k);
                m++;
                ok=1;
            }
            while(pilha.size()!=0 && pilha.top()==m)
            {
                pilha.pop();
                m++;
                ok=1;
            }
            while(i==m)
            {
                if(pilha.size()==0)
                {
                    printf("yes\n");
                }
                else if(pilha.size()!=0)
                {
                    printf("no\n");
                }
                break;
            }
        }
    }
    return 0;
}