Developed by Monroe Ingberman to show a specific kind of hand in Slam invitation. It's applied after a major suit response to the other major openning. Opener applies with certain rules.
Opener should support Responder's suit with at least 4 cards.
Opener should have the Ace of one of the other two suits.
The fourth suit should be void or singleton in Opener's hand.
Opener should have at least 19 points.
If the rules are okey then the Opener bid his suit having the Ace at fourth level. This is a Slam invitation.