H, W = map(int, input().split())
S = [input() for _ in range(H)]
T = []
for i in range(H):
    for j in range(W):
        if S[i][j] == '#':
            T.append((i, j))

if not T:
    print('NO')
    exit()


def solve(h, w):
    seen = {t: 0 for t in T}
    for t in T:
        if seen[t]:
            continue
        seen[t] = 1
        nt = t[0]+h, t[1]+w
        if nt not in T:
            break
        if seen[nt]:
            break
        seen[nt] = 1
    else:
        return 1
    return 0


for i in range(H):
    for j in range(-W+1, W):
        if solve(i, j):
            print('YES')
            exit()
else:
    print('NO')