#include <stdio.h>
#include <string.h>
#include <assert.h>
int H, W;
char str[100];
char board[100][100];
char shiftedboard[100][100];
char tmpboard[100][100];

void copyboard(char src[][100], char dst[][100]){
    for(int x = 0; x < 100; x++){
        for(int y = 0; y < 100; y++){
            dst[x][y] = src[x][y];
        }
    }
}

int countboard(char  b[][100], int num){
    int cnt=0;
    for(int x = 0; x < 2*W; x++){
        for(int y = 0; y < 2*H; y++){
            if(b[x][y]==num) cnt++;
        }
    }
    return cnt;
}
void printboard(char b[][100]){
    /*
    for(int y=0; y < H; y++){
        for(int x =0; x < W; x++){
            printf("%d",b[x][y]);
        }puts("");
    }
    puts("--");
    */
}
void shift(int shift_x, int shift_y){
    assert(shift_x + W < 100 && shift_y + H < 100);
    memset(shiftedboard,0,sizeof(shiftedboard));
    
    for(int x = 0; x < W; x++){
        for(int y = 0; y < H; y++){
            shiftedboard[x][y] += board[x][y];
            shiftedboard[x+shift_x][y+shift_y] += board[x][y];   
        }
    }
    printboard(shiftedboard);
}
int main(void){
    scanf("%d %d",&H,&W);
    memset(board,0,sizeof(board));
    memset(tmpboard,0,sizeof(tmpboard));
    for(int i = 0; i < H ; i++){
        scanf("%s",str);
        for(int j = 0; j < W; j++){
            board[j][i] = (str[j]=='#')? 1 : 0;
        }
    }

    int cnt_one = countboard(board, 1);
    printboard(board);
    
    int shift_x, shift_y;
    for(shift_x = 0; shift_x < W; shift_x++){
        for(shift_y = 0; shift_y < H; shift_y++){
            shift(shift_x,shift_y);
            //printf("count2=%d,cnt_one=%d\n",countboard(shiftedboard,2),cnt_one);
            if(countboard(shiftedboard,2) * 2 == cnt_one){
                copyboard(board,tmpboard);
                for(int x = 0; x < W*2; x++){
                    for(int y = 0; y < H*2; y++){
                        if(shiftedboard[x][y]==2){
                            tmpboard[x-shift_x][y-shift_y] += 1;
                            tmpboard[x][y] = 2;
                        }
                    }
                }
                //printf("candidate shiftx=%d shifty=%d\n",shift_x,shift_y);
                printboard(tmpboard);
                if(countboard(tmpboard,2) == cnt_one){
                    puts("YES");
                    return 0;
                }
            }
        }
    }
    
    puts("NO");
    
    
}