Muiderberg convention

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This article concerns contract bridge and uses terminology associated with the game. See Contract bridge glossary for an explanation of unfamiliar words or phrases.

The Muiderberg convention in the card game Bridge is also known as the Dutch Two opening. It is a preemptive opening based on a two-suiter with precisely a fivecard major and a minor suit (fourcard or longer). In Muiderberg the 2♥ opening denotes five hearts and an unknown minor suit, whilst 2♠ denotes five spades and an unknown minor suit.

The partner of the Muiderberg opener can take the following actions:

  • pass (with tolerance for the opened suit)
  • bid 3♣ (a pass-or-correct bid)
  • bid 3♦ to invite for game in the major suit
  • bid 2♠ (over 2♥) as a contract improvement (opener is allowed to raise with a suitable hand)
  • bid 3♥/♠ (opener's suit) as a preemptive raise
  • bid 3♠/♥ (other major) which is non-forcing but invitational
  • ask for the minor suit using a 2NT relay bid with a strong hand.

The 2NT response is often defined as forcing to game, for example in Biedermeijer and AcolPlus. In particular, with a strong hand with an own suit, responder must bid 2NT first as there is no other way to establish a force. The Muiderberg opener can respond in several ways to the 2NT answer:

  • bid 3♣ with a minimum and clubs / with a four-card clubs
  • bid 3♦ with a minimum and diamonds / with a four-card diamonds
  • bid 3♥ with a maximum and clubs / with a five-card or more clubs
  • bid 3♠ with a maximum and diamonds / with a five-card or more diamonds
  • bid 3NT with 4-4 in both minors
  • bid 4♣/♦ with a 6-card in the bid suit

Both approaches are equally popular.

In competition, 3♣ is natural (opener is expected to pass) while 2NT asks for opener's minor suit and is not necessarily strong. Further, 4♣/♦ are defined as fit-bids in competition.

This convention is named after the Dutch village Muiderberg, the residence of the designers of this two-level opening (Onno Janssens and Willem Boegem).

A variant known as Lucas two-bids allow for 5 cards or more in the bid suit (diamonds, hearts or spades) and 4 cards or more in a second suit which can be any of the remaining three suits.