Internal Data Structure Simplification Abstraction

[dakusui]

In order to allow to use of external covering array generation engines (ACTS, PICT, AETG, etc.), it is required to introduce an internal data structure, where user-facing factors and levels are represented by primitive data types compatible with major engines.
This effort will contain a problem of converting a user-facing constraint, which is written in an arbitrary Java method into a predicate represented only by a handful of logical operators and mathematical comparators which all major tools support.