h,w=map(int,input().split())
g=[input() for i in range(h)]
cnt=0
for i in range(h):
    for j in range(w):
        if g[i][j] == '#':
            cnt+=1
if cnt ==0:
    print('NO')
    exit()

for zure in range(1,w):
    f=[[0]*w for i in range(h)]
    ff=0
    for i in range(h):
        for j in range(w):
            if g[i][j] == '#' and f[i][j] == 0:
                if j+zure >= w:
                    ff = 1
                    break
                if g[i][j+zure] != '#':
                    ff = 1
                    break
                f[i][j+zure] = 1
                f[i][j] = 1
        if ff == 1:
            break

    if ff == 0:
        print('YES')
        exit()

for zure in range(1,h):
    f=[[0]*w for i in range(h)]
    ff=0
    for i in range(h):
        for j in range(w):
            if g[i][j] == '#' and f[i][j] == 0:

                if i+zure >= h:
                    ff = 1
                    break
                if g[i+zure][j] != '#':
                    ff= 1
                    break
                f[i+zure][j] = 1
                f[i][j] =  1
        if ff == 1:
            break

    if ff == 0:
        print('YES')
        exit()


for zure in range(1,min(h,w)):
    f=[[0]*w for i in range(h)]
    ff=0
    for i in range(h):
        for j in range(w):
            if g[i][j] == '#' and f[i][j] == 0:                        
                if i+zure >= h or j + zure >=w:
                    ff = 1
                    break
                if g[i+zure][j+zure] != '#':
                    ff = 1
                    break
                f[i+zure][j+zure] = 1
                f[i][j] = 1
        if ff == 1:
            break

    if ff == 0:
        print('YES')
        exit()

print('NO')