# WA出た、たとえばS['.#', '#.']のときに変化幅はマイナスになるな

H, W = map(int, input().split())
S = []
dots = []
for i in range(H):
    temp = list(input())
    S.append(temp)
    for j in range(W):
        if temp[j] == '#':
            dots.append((i, j))

#print(S)
#print(dots)

dots_set = set(dots)
ans = 'NO'

for di in range(0, H):
    for dj in range(-W+1, W):
        if di==0 and dj==0:
            continue
        covered = set()
        test = True
        for i, j in dots:
            if (i, j) in covered:
                continue
            #print('i', i, 'j', j, (i+di, j+dj) in dots_set, test)
            if (i+di, j+dj) in dots_set:
                covered.add((i+di, j+dj))
            else:
                test = False
            covered.add((i, j))
        #print('di', di, 'dj', dj, covered, test)
        if test == True:
            ans = 'YES'
print(ans)