H,W = map(int,input().split())
S = [input().strip() for i in range(H)]
black = []
for i in range(H):
	for j in range(W):
		if (S[i][j] == "#"):
			black.append((i,j))
		else:
			pass

if (len(black) < 2):
	print("NO")
	exit()

#黒座標を集合に変換
black_base = set(black)
#基準設定
base_x,base_y = black[0]

for (x,y) in black:
	dx = x - base_x
	dy = y - base_y
	
	check = True
	for (p,q) in black:
		dp = p + dx
		dq = q + dy
		
		if ((dp , dq) not in black_base):
			check = False
			break
		
	if (check == True):
		print("YES")
		exit()

print("NO")