H, W = map(int, input().split())
c = []
for _ in range(H):
    c.append(list(input()))
for i in range(H):
    for j in range(W):
        if i == j == 0:
            continue
        b = set()
        f = False
        for x in range(H):
            for y in range(W):
                if x+i>H-1 or y+j>W-1:
                    if (x, y) not in b and c[x][y] == '#':
                        f = True
                        break
                    else:
                        continue
                if c[x][y]=='.' or (x, y) in b:
                    continue
                b.add((x, y))
                if c[x+i][y+j] == '.':
                    f = True
                    break
                else:
                    b.add((x+i, y+j))
            if f:
                break
        if not f:
            print('YES')
            exit()
print('NO')