Improve Code Quality

- Rename some predicates to be more descriptive. Some issues are:
  - `spec_predicate_recursive`: not really recursive from a user perspective
  - take `aux`from the auxiliar predicates
  - `spec_and` and  `and`
  - `or` and `or2`
- Better module structure
  - too much interleaving
  - make them smaller?
- More Tests
  - test coverage not high enough
  - check more scenarios