from copy import deepcopy as dcp
def check(di,dj):
	m = dcp(M)
	for i in xrange(H):
		for j in xrange(W):
			if m[i][j] == "#":
				ni = i + di
				nj = j + dj
				if 0 <= ni < H and 0 <= nj < W and m[ni][nj] == "#":
					m[ni][nj] = "."
				else:
					return False
	return True
H,W = map(int,raw_input().split(" "))
M = [list(raw_input()) for i in xrange(H)]
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"