import sys
read = sys.stdin.buffer.read
readline = sys.stdin.buffer.readline
readlines = sys.stdin.buffer.readlines

from math import gcd
import itertools

H,W = map(int,readline().split())
data = ''.join(read().decode().split())

def test(a,b):
    # ax + by = const 上をまとめる
    words = [[] for _ in range(5000)]
    for x,y in itertools.product(range(H), range(W)):
        key = a * x + b * y
        words[key].append(data[W*x+y])
    for w in words:
        if ''.join(w).replace('##','').count('#'):
            return False
    return True

answer = 'YES' if any(test(a,b) for a in range(50) for b in range(-50,50)) else 'NO'
print(answer)