h, w = map(int, input().split())
S = [input() for i in range(h)]

for di in range(h):
    for dj in range(w):
        if di == 0 and dj == 0:
            continue
        C = [[-1]*w for i in range(h)]
        flag = True
        for i in range(h):
            for j in range(w):
                if S[i][j] == '#' and C[i][j] == -1:
                    C[i][j] = 0
                    ni, nj = i+di, j+dj
                    if 0 <= ni < h and 0 <= nj < w:
                        if S[ni][nj] == '#' and C[ni][nj] == -1:
                            C[ni][nj] = 1
                        else:
                            flag = False
                            break
                    else:
                        flag = False
                        break
        if flag:
            print('YES')
            exit()
else:
    print('NO')