a, b = map(int, input().split(' '))
sq = [input().strip() for i in range(a)]
sq2 = [c for k in sq for c in k]
ans = 'NO'

m_l = 0
m_r = 0
for c in sq:
    if '#' in c:
        m_l = max(c.index('#'), m_l)
        m_r = max(c[::-1].index('#'), m_r)

if ('#' not in sq2) or sq2.count('#') % 2 == 1:
    print('NO')
    exit()
 
for h in range(a):
    for w in range(-m_l, m_r+1):
        sq3 = list('0'*len(sq2)) 
        for t in range(len(sq2)):
            if sq[t//b][t%b]=='#' and 0 < t%b+w < b and 0 < t//b+h < a:
                if sq[t//b+h][t%b+w] == '#' and sq3[t]=='0':
                    sq3[t] = '1'
                    sq3[t+w+(b*h)] = '1'

        if sq2.count('#') == sq3.count('1'):
            ans = 'YES'
            break

print(ans)