def main():
    h, w = map(int, input().split())
    s = [input() for i in range(h)]

    black = []
    for i in range(h):
        for j in range(w):
            if s[i][j] == "#":
                black.append((i, j))

    if len(black) > 0:
        cor = black[0]
        for i in range(1, len(black)):
            cor2 = black[i]
            d1, d2 = cor2[0] - cor[0], cor2[1] - cor[1]
            check = [[0 for k in range(w)] for i in range(h)]

            for j in range(1, len(black)):
                if i != j and check[black[j][0]][black[j][1]] == 0:
                    if 0 <= black[j][0]+d1 < h and 0 <= black[j][1]+d2 < w:
                        if s[black[j][0]+d1][black[j][1]+d2] == "#":
                            check[black[j][0]][black[j][1]] = 1
                            check[black[j][0]+d1][black[j][1]+d2] = 1
                            continue
                    break

            else:
                print("YES")
                break

        else:
            print("NO")

    else:
        print("NO")


if __name__ == '__main__':
    main()