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Challenge.

The game played by this program is based on the game challenge described
by the bridge journalist Hubert Phillips.
To quote from his description:
"Challenge is a game of pure skill.
Here two players play erlternately, as in chess; and, as in chess, the
player will win who can calculate accurately for the larger number of
moves ahead.
The mental processes required for challenge are, indeed, very similar
to the mental processes required for chess.
This is not true of any other card game."
He further relates how the game was introduced to the university of Cambridge
by Profeddor A.S.Besicovitch, under the russian name "Svoyi Koziri".
Apparently Cambridge is the only place where it has been played.

The game played by the program differs from the original game in only one
sense as will be shown below.
Although this change changes the nature of the game a bit, it is (at least
in our opinion) not easier than the original.
It requires as much skill, and we think it is even a bit harder.

The mechanics of the game.

Challenge in its standard form is played with a pack of 32 cards, each suit
consists of eight cards: Aces downto 8's.
It is also possible to play it with packs of 28, 24 or even less cards to
make a simpler game.
Of course also more than 32 cards can be used for a more difficult game.

First the dealer nominates one suit - it does not matter which - as his
trumps, next the non-dealer nominates another suit as his trumps (note
that the players have different trumps), and lastly the dealer nominates
one of the remaining suits as secondary suit.
This last is not important for the game itself, but only for the deal.
To make the program simpler, within the program the computer has always
Spades as his trump suit while the opponent always has Hearts as trumps.

Next the dealer shuffles the cards and takes 16 cards (or half the pack if there
are less or more than 32 cards).
From these 16 cards the dealer takes all his trumps and all the cards
of his secondary colour.
The non-dealer takes all dealers trumps and dealers secondary cards from
the remaining 16 cards.
Next the non-dealer selects from his trump suit the cards corresponding
to the cards the dealer has from the dealers trump suit, and the same
happens with the fourth colour corresponding to the dealers secondary
colour.
The dealer now takes the remaining cards.
After this the hands of dealer and non-dealer are symmetric.
Thus if dealers trumps are Spades and his secondary colour are Clubs,
and non-dealers trumps are Hearts, dealer might have:
	Spades  : A Q 10 8
	Clubs   : Q 10 8
	Diamonds: A K J 9 7
	Hearts  : K J 9 7
and non-dealer has in this case (exactly corresponding):
	Hearts  : A Q 10 8
	Diamonds: Q 10 8
	Ckubs   : A K J 9 7
	Spades  : K J 9 7
Note that it might occur that you do not have any trumps, but in that
case the other party will also not have any trumps!

Now play begins, non-dealer lays a card face upwards on the table.
Dealer now must either play a better card, or pick up the card from
the table.
By a 'better card' is meant a higher card of the suit of the card
on the table, or one of his trumps.
Of course if the card lead is one of his trumps, he has to play a
higher trump.
There is no obligation to play a better card, or to follow suit.
Now players alternate moves, each either playing a better card
or taking the cards on the table, not only the last-played card,
but all the cards on the table.
The object of the game is to play your last card.

Here the game played by the program differs a bit from the original.
In the original game a player who played a better card immediately
lead a new card; in the programs version if a player plays a better
card that is the end of his turn, and he does not lead.

In normal play amongst humans you see only the cards that you have
in your hands and the card on top of tha stack on the table, so it
is a bit easier for the player with the better memory.  As the
computers memory is apparently quite good, and this would give the
computer a vere high advantage, the program displays not only your
cards during play, but also the cards the computer has and the
cards on the table.

The program.

The calling sequence for the program is:
	challenge -ssize -ddepth -afile -ooptions
the parameters have the following meaning:
	-ssize		size is one of the digits 1 to 8.  This
			parameter defines the size of the pack of
			cards to be used.  With -s1 only aces are
			used, with -s8 a complete pack of 32 cards.
			The default is 8.

	-ddepth		depth is a number larger than or equal to 0.
			This parameter specifies the search depth for
			the computers strategy.  Decreasing depth
			simplifies the game, while increasing it makes
			it more difficult (at the expense of time of
			course).  -d0 is very simple to play agains.
			The deault is 4.

	-ooptions	options is a string of letter, each identifying
			a program toggle.  Specifying a letter will
			toggle the associated option.  See below for the
			toggles that are present, and what they do.
			-ohh toggles the 'h' toggle twice and is effectively
			a no-op of course.

	-afile		here file is a filename or empty.  With this option
			analysing mode is entered; see below for details.

When the program is entered you are asked for commands.  When it is your
turn you may:
1.	nominate a card to be played.  You specify a card by giving its
	suit and its value; order and case are not significant.  You may
	indicate tens by '10', 't' or 'x' and aces by 'a' or '1'.  So
	the 10 of spades may be specified as S10, ts or Xs or some other
	variation.
2.	tell that you want to pick up the cards on the table.  You do this
	with the command 'p'.
3.	use one of the extended commands shown in the window in the upper
	right corner of your screen; they are all prefixed by a exclamation
	mark.
4.	If you enter a question mark the program will show you the cards
	you cand play.
5.	When in analysing mode there are two more commands available;
	see below for details.

Analysing mode.

You enter analysing mode either with the -a parameter on the command
line or at the and of a game by entering the 'a' reply.  There are
two forms of analysing mode:
normal:	You enter this mode if you reply 'a' at the end of a game of
	when you give a filename on the command line.  You will be
	put in control again at the end of the game (if a file is
	given, the game is read in from that file), and you can play
	with it using the commands above and the auxiliary commands
	below.
setup:	You enter this mode if you give the -a option, but no file
	name on the command line.  The program will put you in control
	with all the cards in your hand, and no cards on the table or
	in the computers 'hand'.  By playing cards and letting the computer
	pick up (he must if you do this correctly), you can achieve
	every starting position.
The following auxiliary commands are available in this mode:
6.	'b' for back up.  Backs up one move for both you and the computer.
7.	'z' for pass.  Pass the move to the computer again.  This is useful
	in setup mode if you have achieved the hand you wanted and the
	computer should start.

Extra commands.

A number of extra commands are available.  The set depends on the mode
you are playing in.  A list of commands is given in the window in the
upper right corner of your screen.  The following commands are possible:
!a	When in analysing mode: return to game mode, read in next game,
	or set up next game.
!c	When in analysing mode: consult the computer for a suggested move.
!d	When in game mode: proprose a draw.  This may only be given if
	the table is empty.
!f	Announce you have a forced win.  This may only be announced if the
	table is empty.  The program is very conservative in deciding whether
	a given hand is a forced win!
!h	Toggles the 'h' toggle.  If on, the program will mark the cards
	you may play on every turn (this is equivalent to entering a question
	mark on every turn).
!i	Give instructions.
!l	Toggles the 'l' toggle.  If on, the game will be logged onto the
	file 'challenge.log', for subsequent use by the program in
	analysing mode.  If this toggle is put on during a game, the game
	will be logged from the start.
!r	Resign.  Normally this is accepted.
!s	Go into a sub-shell.
!w	Toggles the 'w' toggle.  If on, the extra commands window is not
	displayed (although the commands are still available of course).
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