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'

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