Sim
Lay a string a turn. Close a triangle of your own colour and you lose. Best of 3 games.
Sim is a two-player pencil-and-paper game in which you take turns drawing a line in your colour between six points. The player who first completes a triangle entirely in their own colour loses, and mixed-colour triangles are safe.
Six brass pins on a cork board and fifteen lines between them. Take turns stretching a string of your colour along one line. There is nothing to chase, only something to avoid: close a triangle all in your own colour and you lose.
Also known as Sim pencil game, Sim (pencil game), Triangle game.
- How you hold it
- Face-off
- Match
- Best of 3 games
- Length
- About 40 to 80 seconds a game
- Play
- Friend or bot
How to play Sim: quick rules
About 40 to 80 seconds a game with 6 pins, 2 to 4 minutes for best of 3; 8 pins takes about twice as long. Full rules, options and bot levels are further down.
- 1Take turns stretching a string between two pins.
- 2Close a triangle of your own colour and you lose.
- 3Mixed triangles are safe.
- 4Knots mark the lines that would lose for you.
Sim rules
Setup
- The board has 6 pins on a ring by default (7 or 8 are options), with every line between two pins pencilled in: 15 lines on 6 pins, 21 on 7 and 28 on 8.
- A coin toss picks who lays the first string of a fresh match; on a rematch the previous loser starts. After each game, the loser starts the next.
- A 3-2-1 countdown starts each game.
Turns
- On your turn, lay exactly one string in your colour on any open line. There is no pass and no undo.
- If your string completes a triangle whose three sides are all your colour, you lose the game at once.
- Triangles with mixed colours are harmless, and so is any triangle with a grey string in it.
Grey string
- With Grey string on, each player may lay one grey string per game instead of a coloured one. It belongs to nobody and never counts toward a triangle.
- Tap the grey spool in your dock to arm it, then tap a line. Tap the spool again to put it back. Arming lasts only for that turn.
Winning
- A game ends when a player closes a triangle of their own colour; the other player wins it.
- Without grey strings, a game can't be drawn: a full board on 6, 7 or 8 pins always contains a one-colour triangle.
- With grey strings, a full board with no one-colour triangle is possible. That game is replayed with the other player starting and doesn't count.
- A match is a single game, best of 3 (the default) or best of 5. It never ends drawn.
Hints against the bot
- Playing the bot outside a tournament, you can spend 20 coins on a hint on your turn. It rings, for two seconds, the line the Hard bot would lay for you. If you are cornered but still hold your grey string, it points to the grey string instead.
- A hint never lays the string for you, and you can take one per turn. If you are cornered with no grey string, nothing is shown and no coins are spent. There are no hints against a friend or in a tournament.
Tips to win at Sim
- 1Think of it as keeping safe lines, not taking good ones. The player who runs out of safe lines first loses.
- 2Spread your strings out. Lines of your colour that share a pin are the start of a triangle, so avoid building up one pin.
- 3Use your rival's strings as shields: a triangle with even one of their lines in it can never hurt you.
- 4Count the knotted lines. When most open lines are dangerous for your rival and few are for you, you're winning.
- 5With 6 pins the second player can always win with perfect play, so starting second is no disadvantage.
Where Sim comes from
Sim was invented by the American mathematician Gustavus Simmons in 1969. It is based on a result from Ramsey theory: with six points and two colours, every full board must contain a one-colour triangle, which is why the game can't end in a draw.
Controls
Phone flat between you. Each player owns a half, and the far half faces the far player.
- Tap a line to lay your string on it. The touch finds the nearest open line, so you don't need to hit the thin pencil mark.
- Or tap a pin, then a second pin. The picked pin pulses and every pin it can still join glows; tap it again to drop it.
- A line tap lays the string straight away, so use the two-pin path if you want to check first.
- The phone lies flat between you; each player's dock, with their spool of yarn, sits at their own end.
Options
Every option is free. Defaults are marked.
| Option | Choices | What it does |
|---|---|---|
| Pins | 6 (default)78 | Classic, Wider or Big board. More pins means more lines and longer games. |
| Games | SingleBest of 3 (default)Best of 5 | How many games to win the match. |
| Danger knots | On (default)Off | Extra: on your turn, every line that would close your own triangle is dashed with a knot. It shows only what the rules make certain, never a best line, and works the same for both players. |
| Grey string | OnOff (default) | Extra: one grey string each per game that belongs to nobody. |
Play Sim against the bot
The bot plays Blue and sees the whole board, as you do. It tries to keep plenty of safe lines for itself and leave you few. It pauses to think before each string.
Easy
Sometimes lays a string without checking it's safe, so it can lose by accident. It never uses the grey string.
Normal
Picks the safe line that leaves it the most room compared with you, looking one move ahead, and now and then picks any safe line. Cornered, it uses its grey string if it has one.
Hard
Looks several moves ahead on 6 pins (fewer on bigger boards) and plays its grey string where it hurts you most. It still slips on rare occasions.
Online, tournaments and hints
- Online
- PlannedOnline play for Sim is planned, not available yet. Today you play a friend on the same phone or the bot.
- Tournament
- Can be drawn in a tournamentIn a tournament it plays the default options: 6 pins, best of 3, Danger knots on. Hints are off.
- Hints
- Stuck against the bot? A hint lights up the strongest move for a few coins. Never with a friend, online or in a tournament.
Coming soon
- Online play. Play Sim against someone on another phone, with a turn clock.
How it feels
- A brass tick when you pick a pin and a soft pluck as the yarn winds from pin to pin.
- A low boing on the yarn when someone closes their own triangle: the three strings blink and the triangle shakes.
- A stamped sticker between games naming the next one.
Accessibility
- Colour is never the only cue: Blue's yarn has a tighter twist than Red's, grey strings are dashed, and losing lines carry a knot.
- Two ways to lay a string, a line tap or two pin taps, both with one finger.
- With reduce motion on, strings appear at once, the losing triangle shades without blinking or shaking, and nothing pulses.
- Every line and pin has a screen-reader label, and knotted lines are read as "closes your triangle".
- There is no clock on a turn against a friend or the bot.
Sim questions
Take turns drawing one line in your colour between any two of six points. Whoever completes a triangle with all three sides in their own colour loses.
No. On six or more points every full board contains a one-colour triangle, so someone always loses. Only the optional grey string can leave a board without one, and that game is replayed.
A coin toss decides the first game of a fresh match, and after that the loser of each game starts the next.
Avoid piling your strings onto the same pins and use your rival's strings to break up your triangles. Aim to keep more safe lines for yourself than your rival has.
Yes. Sim in Duo Clash is built for two players on the same phone. Phone flat between you. Each player owns a half, and the far half faces the far player.
Yes. The bot plays Blue and sees the whole board, as you do. Choose Easy, Normal or Hard.
Play Sim on one phone
Free on Android. Sit face to face, or take on the bot on Easy, Normal or Hard.
