import itertools
import copy
h, w = map(int, input().split())
start_x, start_y = None, None

field = [list(input()) for _ in range(h)]
black_n = "".join(map("".join, field)).count("#")

if black_n > 0 and black_n % 2:
    print("NO")
    exit()


def check(y, x):
    global start_x, start_y
    if field[y][x] != "#":
        return False
    if start_x is None:
        start_x = x
        start_y = y
    dx, dy = x - start_x, y - start_y
    m = copy.deepcopy(field)
    for red_y in range(h):
        for red_x in range(w):
            if m[red_y][red_x] == "#":
                m[red_y][red_x] = "@"
                nx = red_x + dx
                ny = red_y + dy
                if ny >= h or nx >= w or m[ny][nx] != "#":
                    return False
                m[ny][nx] = "@"
    return True



for i in range(h):
    for j in range(w):
        if check(i, j):
            print("YES")
            exit()
print("NO")