Gomoku & Renju Glossary — Fours, Open Fours, the Four-Three, VCF, and the Forbidden Moves

The VCF puzzles and explanations here are full of special terms — four, open three, four-three, VCF, forbidden moves. Once you know what they mean, your understanding changes completely, so here are the most common ones in plain English; dip in wherever you like. Note that this site's board uses free-style gomoku (no forbidden moves); renju's forbidden moves are explained at the end and in the related columns.

Five in a row — the winning shape

Lining up five of your stones in a row — vertically, horizontally, or diagonally — wins. That is the goal of gomoku and renju. Every attack and defence exists to make your own five first, or to stop your opponent's.

Four (shi) — a move that forces a block

Four stones that are one move away from five form a 'four.' To prevent five, the opponent must block the open end. A four is the strongest forcing move, and chaining fours to keep attacking is VCF (below).

Open four (katsu-shi / tatsu-shi) — an unstoppable four

A four that is open at both ends is an 'open four.' Since playing either end makes five, the opponent can block only one side and cannot stop it — a win on the spot. It is one of the goals of a four-chase.

Three / open three (katsu-san) — a threat you can't ignore

Three stones in a row form a 'three.' An open three (open at both ends) is especially dangerous: if ignored it becomes an open four next and can no longer be stopped, so the opponent is forced to respond. A three is one step short of a four.

Broken three / broken four — shapes with a gap

Stones spread out with a one-space gap. For example, ●●_● becomes a four when you fill the gap (a broken three), and ●●●_● becomes five when filled (a broken four). Even without being consecutive they are real threats, so don't overlook gapped shapes.

Four-three (shi-san) — winning with two threats

A single move that makes a 'four' and an 'open three' at the same time is a 'four-three.' The opponent must block the four, and meanwhile the three grows into a four, then five. Two threats cannot both be stopped, so it wins. The decisive blow in VCF is making this four-three (or an open four) as a double threat.

VCF (continuous fours) — winning by chasing with fours

VCF (Victory by Continuous Fours) is an attack that keeps forcing the opponent to block fours, then finishes with a four-three or open four for a double threat. This site's VCF puzzles are positions, verified by exhaustive search, where this four-chase forces a win.

Forbidden moves (kinte) — banned for Black only in renju

In renju, the first player (Black) alone has three moves that are not allowed — double-three, double-four, and overline. The rule curbs Black's advantage to keep the game even; White has no such restrictions. As an exception, when a move completes exactly five, the win takes priority over the ban.

Double-three, double-four, overline — the three forbidden moves

Double-three (san-san) is one move making two open threes at once. Double-four (shi-shi) is one move making two fours at once. Overline (cho-ren) is Black making six or more in a straight line — in renju, Black can win only with exactly five. Each is a loss for Black in renju.

Free gomoku vs renju (this site's rules)

Free-style 'gomoku' has no forbidden moves; 'renju' adds the double-three, double-four, and overline bans for Black. This site's VCF board runs on free-style gomoku rules and does not adopt the forbidden moves. So a winning line may include a double-four (one move making two fours), which is legal under gomoku rules. For a full explanation of the forbidden moves, see the related column on renju's forbidden moves.