# -*- coding:utf-8 -*-

def paint(k,l):
	global h,w,C
	isPainted = [[False for i in xrange(w)]for j in xrange(h)]
	for i in xrange(h):
		for j in xrange(w):
			if isPainted[i][j]:
				continue
			isPainted[i][j] = True
			if C[i][j] == "#":
				if i+l >= 0 and i+l < h and j+k >= 0 and j+k < w:
					if  C[i+l][j+k] == "#" and not isPainted[i+l][j+k]:
						isPainted[i+l][j+k] = True
					else:
						return False
				else:
					return False
	return True

if __name__ == "__main__":
	h,w = map(int,raw_input().split())
	C = [raw_input() for i in xrange(h)]
	minx, miny = -1,-1
	for i in xrange(h):
		for j in xrange(w):
			if C[i][j] == "#":
				minx,miny = j,i
				break
		if minx != -1:
			break
	if minx == miny == -1:
		print "NO"
		exit()
	for i in xrange(-minx,w-minx):
		for j in xrange(h-miny):
			if paint(i,j):
				print "YES"
				exit()
	print "NO"