H, W = map(int,input().split())
D = []
for i in range(H):
    D += input().split()
D = [c for l in D for c in l]
if '#' not in D:
    print('NO')
    exit(0)
for i in range(1, H * W):
    T = D[:]
    R = -1
    for j in range(len(T)):
        if T[j]=='#':
            if j + i < len(T) and T[j + i] == '#' and (R == (j + i) // W - j // W or R == -1):
                T[j], T[j + i]='.', '.'
                R = (j + i) // W - j // W
            else:
                break
    else:
        print('YES')
        break
else:
    print('NO')