H, W = map(int, input().split())
S = [input() for _ in range(H)]

for dx in range(H):
    for dy in range(-W-1, W):
        if dx == 0 and dy <= 0:
            continue
        
        flag = [[-1 for _ in range(W)] for _ in range(H)]
        
        for i in range(H):
            for j in range(W):
                if S[i][j] == '#' and flag[i][j] == -1:
                    if i+dx < H and 0 <= j+dy < W and S[i+dx][j+dy] == '#':
                        flag[i][j] = 0
                        flag[i+dx][j+dy] = 1
                    else:
                        break
            else:
                continue
            break
        else:
            print('YES')
            exit()

print('NO')