H, W = map(int, input().split())
G = [list(input()) for i in range(H)]

break_flg = False
for d in range((H + 1) // 2):
    for r in range((W + 1) // 2):

        if (d == 0) and (r == 0):
            continue

        T = [[0 if G[i][j] == '#' else -1 for j in range(W)] for i in range(H)]
        for i in range(H):
            for j in range(W):
                if T[i][j] == 0:
                    if not ((0 <= i + d < H) and (0 <= j + r < W)):
                        break_flg = True
                        break

                    if T[i + d][j + r] == 0:
                        T[i + d][j + r] += 1
                    else:
                        break_flg = True
                        break

            if break_flg:
                break_flg = False
                break

        else:
            print('YES')
            exit()

print('NO')