[Rule] EXACT COVER BY 3-SETS to SUBSET PRODUCT

**Source:** EXACT COVER BY 3-SETS
**Target:** SUBSET PRODUCT
**Reference:** Garey & Johnson, SP14, p.224

## Specialization Note

This rule's source problem (EXACT COVER BY 3-SETS / X3C) is a specialization of MINIMUM SET COVERING. Implementation should wait until X3C is available as a codebase model.