A Brief look at Connect-Five

After more than a decade's hiatus from Connect-Four, I got interested in the Connect-Five variant. Players place TWO stones at each turn and try to get FIVE in a row. To even things out, we usually play that the very first (and therefore of necessity the very last) moves are of single stones. Red will play first; White second. In the simplest situations, where only one or two columns are active, Major threats (MT) appear to obey the following rules, if applied in order:

I won't try to explain things in excruciating detail -- Buy the Connect-Four book if you want excruciation! -- But tactical ideas arise which do not exist when players can only drop one stone at a time.

Examine this position:

Diagram 1
White to play, and mate in 2
 
6      
5  
4      
3      
2  
1  
 ABCDEFG

Moves: (1) D (2) dd (4) DD (6) cc (8) CC (10) bb (12) EE (14) bc! (16) BC (18) ee (20) BB (22) gg (24) DE? (26) ef (28) AA (30) af! (32) AA


  The White move (34) fg! wins. He is threatening to seize victory at f5, and is also threatening a vertical win in the G-column. Red cannot stop both threats. The stones at f1 and f2 are White, but this is irrelevant.

Note the empty cell at A6. Because one empty cell is just half a move, this empty cell implies a sort of `Zugzwang reversal' not seen in the One-Stone-At-A-Time game.

Once White has g1 and g2, and both f1 and f2 are occupied, White's winning move f3-g3 will always seem to be available. Black cannot block it: G3 allows g4-g5 and a double F-column threat, and Red F3 loses at once. Yet if Red can keep White busy, the move parity will be wrong for White to make this move in the endgame.

Red has made a subtle error in the run-up to Diagram 1. Let's backtrack.

Diagram 2
Red to play, with a single move to salvage a Draw
 
6          
5        
4        
3        
2      
1      
 ABCDEFG

Moves: (1) D (2) dd (4) DD (6) cc (8) CC (10) bb (12) EE (14) bc! (16) BC (18) ee (20) BB (22) gg


 

(24) AA almost works. But (26) ad! (28) AA (30) ff! (32) EE (34) fg! leads to the same win we saw in Diagram 1.

Only (24) AD salvages the Draw. The game might then continue (26) af (28) AA (30) af (32) EE with White unable to play the winning (34) because he must block the Checkmate at A6.

Suppose White plays (26) ff after (24) AD, so that he needs only two more stones for the same win he gets in Diagram 1:

Diagram 3
White to play and Draw
 
6        
5        
4        
3      
2  
1  
 ABCDEFG

Moves: (1) D (2) dd (4) DD (6) cc (8) CC (10) bb (12) EE (14) bc! (16) BC (18) ee (20) BB (22) gg (24) AD! (26) ff (28) AA!


 

White would win by playing (30) ef ... except that he first must block Red's impending win in the A-column ... and then block a Red 6th-row win on the next turn.

Once White gets g1-g2 in these variations, Red must play with care. He cannot play G3: White responds g4-g5 and gets adjacent major threats at F4 and F5. Red must exploit his threats in the A-column and 6th row to avoid the Zugzwang reversal we noted in Diagram 1.

Here's another Game with the same theme. Starting from the same opening DddDDccCCbbEE, suppose White plays (14) ee? instead of bc! Red wins by grabbing the 5th-row: (16) CE! Suppose White plays (18) gg (20) BG (22) gg, getting the same double F-column threat he sought before.

But Red prevails with (24) BE! (26) aa (28) AB! (30) aa This may seem counter-intuitive: Red establishes a 5th-row threat but gives it away to (30) aa, but the idea is to prevent White from playing f1/f2 together. Red forces again, e.g. with (32) CD (34) bf and then wins a Zugzwang with (36) AG!

Openings

Opening at D1 is very bad!? !!

My wife and I had been playing for a long while before I suddenly realized that opening in the center with D1 was probably dumb! That stone participates in no diagonals (though d2 and d3 do). Moreover, since FIVE in a row means the C- and E-columns are just as essential to horizontal mates, the D-column lacks the special value it has in Connect-Four.

My wife and I have had some intricate exciting games. Unfortunately, my brain isn't what it once was and I can't remember a game unless I record the moves as we play. Here is one game:
C ee EE ce DD dd DC de FG fg? FF! aa AB bb BB? ab FF? aa! GG gg! CC c.