Responsive double

1m - dbl – 2(3,4)m - dbl = M at least 4-4

1M - dbl – 2(3)M - dbl = m at least 4-4, with oM, we bid it

1m - dbl - 1M - dbl = not responsive; defense against psyche, shows 4 card M

dbl after responsive dbl = strong (not penalty)