def check(di,dj):
	flag = [[True for i in xrange(W)] for i in xrange(H)]
	for i in xrange(H):
		for j in xrange(W):
			if M[i][j] == "#" and flag[i][j]:
				ni = i + di
				nj = j + dj
				if 0 <= ni < H and 0 <= nj < W and M[ni][nj] == "#":
					flag[ni][nj] = False
				else:
					return False
	return True
H,W = map(int,raw_input().split(" "))
M = [list(raw_input()) for i in xrange(H)]
if sum(1 for i in xrange(H*W) if M[i/H][i%H] == "#") == 0:
	print "NO"
	quit()
for j in xrange(1,W):
	if check(0,j):
		print "YES"
		quit()
for i in xrange(1,H):
	for j in xrange(-W+1,W):
		if check(i,j):
			print "YES"
			quit()
print "NO"