GIB: Imperfect Information in a Computationally Challenging Game

TL;DR

This paper presents GIB, a computer program for bridge that incorporates five technical innovations to handle imperfect information and achieve expert-level play, making it the strongest in the world.

Contribution

Introduction of five novel techniques—partition search, Monte Carlo methods, achievable sets, lattice-based alpha-beta pruning, and squeaky wheel optimization—for computer bridge.

Findings

GIB is approximately of expert caliber.

GIB is the strongest computer bridge program to date.

The techniques significantly improve game-playing under imperfect information.

Abstract

This paper investigates the problems arising in the construction of a program to play the game of contract bridge. These problems include both the difficulty of solving the game's perfect information variant, and techniques needed to address the fact that bridge is not, in fact, a perfect information game. GIB, the program being described, involves five separate technical advances: partition search, the practical application of Monte Carlo techniques to realistic problems, a focus on achievable sets to solve problems inherent in the Monte Carlo approach, an extension of alpha-beta pruning from total orders to arbitrary distributive lattices, and the use of squeaky wheel optimization to find approximately optimal solutions to cardplay problems. GIB is currently believed to be of approximately expert caliber, and is currently the strongest computer bridge program in the world.