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 xz in range(h):
    for yz in range(w):
        if 0 == xz and 0 == yz:
            continue
        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+xz >= h or j + yz >=w:
                        ff = 1
                        break
                    if g[i+xz][j+yz] != '#':
                        ff = 1
                        break
                    f[i+xz][j+yz] = 1
                    f[i][j] = 1
            if ff == 1:
                break

        if ff == 0:
            print('YES')
            exit()
            
for xz in range(h):
    for yz in range(w):
        if 0 == xz and 0 == yz:
            continue
        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-xz < 0 or j - yz < 0:
                        ff = 1
                        break
                    if g[i-xz][j-yz] != '#':
                        ff = 1
                        break
                    f[i-xz][j-yz] = 1
                    f[i][j] = 1
            if ff == 1:
                break

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

print('NO')