V.   THREE LITTLE TRUMPS

Vinje hand pattern signals communicate single suit parity. Prism signals seek to communicate both the parity and the identity of the single suit.

Consider this West hand from a previous deal:

8

5

2

J

9

8

6

2

9

4

10

6

3

The message sent- ( 8_2...5)- I am even only in diamonds.

Holding three little trumps (852) and an even single suit:
1.) The trump suit (odd) cannot be the single suit (even.)
2.) Hearts, diamonds, clubs are the single suit candidates.
3.) The relationship of  the third trump to the
     the echo identifies the single suit:
_ Above ...the high candidate.
_ Amid  ...the middle candidate.
_ Below  ...the low candidate. 

Consider the following warm-up   featuring a Major Prism and three little trumps with East:

West leads the club king, won by declarer's ace. Declarer draws trump in three rounds and exits with the club jack, all follow.  East's plays his three (odd) trump spots 10_9...8. The message is I am even in clubs .

The auction indicates that declarer holds a one-suiter with three diamonds. Declarer's hand pattern index is three. The relevant hand pattern: 6-3-2-2. The position with West needing three tricks:

Declarer started with 6=2=3=2. Upon winning the club queen, West cashes the heart ace, exits with a heart, and awaits the setting tricks in diamonds.

The full deal:

Switch red sixes in the diagram on the left. Declarer captures the club king opening  and draws trump. East's plays his three (odd) spades spots 8_9...10. I have an odd single suit...

West cashes the ace of diamonds, exits with a diamond and awaits the setting tricks in hearts.   

The full deal:

In the 1991 World Top Pairs at The Hague, a prizewinning pair misdefended a grand slam in hearts:

West led a club against seven hearts. Declarer won with the king, continued with a club to the ace, and trumped a club in dummy, East following. Declarer ran his seven solid trumps. East held three little trumps.

West had to find a discard on the last trump in what he hoped to be this guess which finesse position: 

Declarer can go wrong by discarding the spade queen on the heart five, crossing to dummy's diamond ace, and finessing the spade jack. Hopefully, West discarded the spade eight.

Disaster. The position above was not the position in reality. In fact, declarer was without recourse until West discarded the spade. North-South: +2210

A defender expecting a prism signal would focus on East's three little trump spots: 10_2...8. The message I am even in diamonds.

The index of declarer's hand pattern is either zero or two. The relevant hand patterns: 7-3-2-1 or 7-3-3-0.

Review

West to discard on declarer's last trump in this position:

A declarer with a 7-3-2-1 hand pattern and 1=7=2=3 distribution has two successful lines: (1) With jack-small of diamonds and stiff ace of spades remaining, discard the diamond queen and execute a non-positional crisscross squeeze.

(2) Without the diamond jack the straight diamond finesse succeeds in the position above. West cannot defend against either line. There is no losing "guess which finesse" option because declarer's 1=7=2=3 allows no spade finesse.

Therefore, West assumes that declarer started with a 7-3-3-0 hand pattern and 3=7=0=3 distribution. He defeats the contract by discarding the diamond eight.

The actual deal:

The "guess which finesse" ending, where declarer can opt to unblock spades by discarding the queen for a losing finesse, arises from this variation:

East   plays his three little trumps 8_2...10. The message I am even in spades.

The index of declarer's hand pattern is two. The relevant hand pattern: 7-3-2-1. Declarer   started with 2=7=1=3 distribution. Baring the spade king is the correct defense in this "guess which finesse" ending. 

Prism signals seek to communicate both parity and identity of the single suit. Three trump spots are used to include two pieces of information in one prism signal. Extra trumps are, of course, welcome.