# coding: utf-8
from collections import deque

H, W = map(int, input().split())
# board[H][W]
board = [list(input()) for __ in range(H)]

sum_char = 0
index_board = []
for ind_h, row in enumerate(board):
    for ind_w, char in enumerate(row):
        if char == "#":
            sum_char += 1
            index_board.append((ind_h, ind_w))


def check(h, w):
    do_board = deque(index_board[:])
    while do_board:
        check_index = do_board.popleft()
        if (check_index[0] + h, check_index[1] + w) in do_board:
            do_board.remove((check_index[0] + h, check_index[1] + w))
        else:
            break
    else:
        return True

    return False

def solve():
    if sum_char % 2 == 1:
        return "NO"

    for h in range(H):
        for w in range(W):
            # print("h: {0}, w: {1}".format(h, w))
            if check(h, w):
                return "YES"
            else:
                continue

    return "NO"


print(solve())