Four Color Theorem and Ssreflect Extension
Georges Gonthier (of Microsoft Research, in Cambridge, England) and Benjamin Werner (of INRIA) used Coq to create a surveyable proof of the four color theorem, which was completed in September 2004.
Based on this work, a significant extension to Coq was developed called Ssreflect (which stands for "small scale reflection"). Despite the name, most of the new features added to Coq by Ssreflect are general purpose features, useful not merely for the computational reflection style of proof. These include:
- Additional convenient notations for irrefutable and refutable pattern matching, on inductive types with one or two constructors
- Implicit arguments for functions applied to zero arguments – which is useful when programming with higher-order functions
- Concise anonymous arguments
- An improved
settactic with more powerful matching - Support for reflection
Ssreflect 1.4 is freely available dual-licensed under the open source CeCill-B or Cecill-2.0 license, and is compatible with Coq 8.4.
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