## Problems (COPS)

### Database

Problem sets used in the competition stem from COPS, a database of confluence problems. Each problem has a unique and persistent number so that you can refer to the problems by e.g. "COPS ♯100". Each problem is equipped with tags, and problems can be queried using a combination of these tags.

### Format

Each problem has one of the following formats. Follow the link to check the details.

- TRS format first-order term rewrite systems
- CSCTRS format context-sensitive conditional term rewrite systems
- CSTRS format context-sensitive term rewrite systems
- CTRS format conditional term rewrite systems
- HRS format higher-order rewrite systems
- MSTRS format many-sorted term rewrite systems

### Submission

Submissions of new problems are welcome. For submission, please use the web interface. Problems should follow one of the formats above. Alternatively, you can send problem files in these formats to the steering committee.

### Structure

Every problem belongs to one of four families.

- literature examples from the literature (articles, papers, theses, technical reports) dealing with confluence
- crafted confluence problems crafted with pen and paper
- generated confluence problems derived by (automatic) transformation techniques, random generators, etc.
- debugging problems where confluence analysis may not be of interest but which are suitable for debugging tools