#include <iostream>

 #define MAXN 600

 using namespace std;

 int _m[MAXN][MAXN];

 int main()

 {

     //freopen("acm.acm","r",stdin);

     int c;

     int r;

     int i;

     int j;

     int sum;

     while(cin>>c>>r,c||r)

     {

     for(i = ; i < r; ++ i)

     {

         for(j = ; j < c; ++ j)

         {

             cin>>_m[i][j];

         }

     }

     for(j = ; j < c; ++ j)

     {

         sum = ;

         for(i = ; i < r; ++ i)

         {

             //sum += _m[i][j];

             if(_m[i][j] == )

             {

                 break;

             }

         }

         if(i == r)

         {

             cout<<"yes"<<endl;

             break;

         }

     }

     if(j == c)

     {

         cout<<"no"<<endl;

     }

     }

 }