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    IV. TWO COUPLE PRISMS

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{8-3-7-8}

{5-6-7-8}

{6-9-6-5}

{5-7-6-8}


Two Couple Prisms are prisms that contain two odd numbers and two even numbers.


Prosecution Exhibit II from the Prologue features a Two Couple Prism:

LP20.gif (18328 bytes)

The prism {8-3-7-8} contains an odd couple and even couple of numbers. The even couple corresponds to the black suits. The odd couple corresponds to the red suits. The prism takes its name from the odd couple. {8-3-7-8} is a Red Prism.

Examine the single suits in the closed hands of Exhibit II:

CHIV11.gif (11313 bytes)

{8-3-7-8}
Red Prism

The concealed single suits are the blacks with relative parity opposite.


Switch the heart four and club four in the closed hands, and examine the resulting relationships:

CHIV12.gif (12162 bytes)

{8-3-7-8}
Red Prism

The concealed single suits are the reds with relative parity equal.

All interchanges of one or more cards between the closed hands bear out these relationships: (1) The concealed single suits corresponds to a prism couple. (2) Relative parity varies with correspondence.


There are six Two Couple Prisms. Each prism takes its name from the odd couple:

Red Prisms and Black Prisms

Major Prisms and Minor Prisms

Pointed (s.gif (111 bytes)/d.gif (109 bytes))Prisms and Round (h.gif (112 bytes)/c.gif (113 bytes)) Prisms


Two Couple Prisms

  • The concealed single suits correspond to a prism couple.

  • Correspondence to the odd couple indicates equal relative parity.

  • Correspondence to the even couple indicates opposite relative parity.


Consider this deal featuring a Round Prism:

CHIV20.gif (18631 bytes) West leads the heart jack, captured by  dummy's king. Declarer plays the ace and king of trump. West with two (even) trumps signals possession of an even single suit- spades, the trump suit itself. Declarer continues with a heart to dummy's queen. East trumps..

 

 

West...Even spades

    Round Prism

Declarer...Odd diamonds

East is on lead in this position, needing one trick:

CHIV21.gif (11177 bytes)

Declarer, who holds four spades and opened 1NT,   holds three diamonds (not five or one.) The index of declarer's hand pattern is three- 4-4-3-2.   

Declarer started with 4=4=3=2 distribution.

Declarer started play with ten tricks: four spades, two hearts and one heart ruff, two diamonds (assume the diamond king), and one club. If declarer can pick up the diamond suit without loss, the two additional tricks fulfill the contract. Conceding one club trick does not harm the defense.

So rather than open up the diamond suit, East exits with a club into the jaws of the tenace, defeating the slam.

The full deal:

CHIV22.gif (21935 bytes)


Switch minor suit nines in the closed hands and the message changes:

CHIV20.gif (18631 bytes)

West leads the heart jack, captured by dummy's king. Declarer plays the ace and king of trump. West with two (even) trumps signals possession of an odd single suit.

Declarer continues with a heart to dummy's queen. East trumps. West signals an (odd) heart start -five.

West...Odd hearts

Round Prism

Declarer...Odd clubs

Declarer's hand pattern index is three- 4-4-3-2.    Needing one trick, East to lead in this position:

CHIV21.gif (10309 bytes)

Declarer started with 4=4=2=3 distribution. The club exit, correct before, yields a club trick after which declarer will trump a club in dummy and claim.

So East exits with a diamond and awaits the setting trick in clubs.

The full deal:

CHIV33.gif (21582 bytes)


Defenders need to know both the parity and the identity of partner's single suit to use a prism effectively. So prism signalers learn to embed the two pieces of information in one communiqué.

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