My "Trapezoid" Opening Theory
Posted: 16 December 2025, 00:39
Below is a game I played as First Player (White) against an AI from https://temhelk.itch.io/yinsh
I get my butt kicked by this AI if I max out its thinking time, so I only gave it a 1-second thinking time. I also know that another player on here was also able to beat the AI (with 1 second thinking time), but not regularly.
In my experience, this AI is an "Edge Player". It concentrates it rings along the edge of the board.

Personally, I am a "Center" player.
Most of the time, my rings will be clustered at the center to form a "trapezoid" where the longer edge of the trapezoid (3 rings) will be along the centerline.
There are a few other characteristics to my opening:
The downside to this "Trapezoid" opening (which a certain player does to annoy me) is when they are the First player and places a ring at the center just to mess with me.
I get my butt kicked by this AI if I max out its thinking time, so I only gave it a 1-second thinking time. I also know that another player on here was also able to beat the AI (with 1 second thinking time), but not regularly.
In my experience, this AI is an "Edge Player". It concentrates it rings along the edge of the board.

Personally, I am a "Center" player.
Most of the time, my rings will be clustered at the center to form a "trapezoid" where the longer edge of the trapezoid (3 rings) will be along the centerline.
There are a few other characteristics to my opening:
- Longest Line of the Board - From the "Trapezoid" opening, I generally play along the "longest line" of the board which is just outside of the centerline. The idea is that this gives me a lot of space to form a line. The other advantage to this line over the centerline is that once your ring reaches the end of the board, that becomes the "starting position" for edge play. It would reach the spot where an Edge Player would have ordinarily played during ring placement. So in the game above, it was hypothetically possible for me to form my second line along the edge instead of the centerline. It allows me to pivot more easily.
- "Wall" Defense - The long-edge of my "trapezoid" functions like a wall to helps shield the line I am forming. The "wall" also serves another defensive purpose which is that whenever someone tries to flip my marker, the "wall" might be able to undo the damage, immediately flipping back.
- Line Orientation - Against an "Edge" Player, I usually avoid having my line parallel to their line. Defensively, this often requires them to spend 2-turns to navigate their ring to sabotage me. Offensively, rings of my line is aimed right at their line.
- Speed - I think Center is a tradeoff between speed and defense. I tend to form a line faster than an edge-player, but it is vulnerable to being sabotaged. However, it is often the case that my opponent abandons their own line formation to sabotage me.
- Easy Next Plan- Generally, once I scored my first ring, my remaining rings are often still lined up and ready to start forming their second line. Very often, my opponent is just about to finish their first line, and I am already starting to form my second line.
The downside to this "Trapezoid" opening (which a certain player does to annoy me) is when they are the First player and places a ring at the center just to mess with me.
