Add some simple theorems in tests

[marfvr]

Proposed changes

Add some simple theorems in the tests. They are tested using Hypothesis to replace the placeholder with "every possible" formula (almost :-) )

Fixes

n/a

Types of changes

What types of changes does your code introduce to agents-tac? Put an x in the boxes that apply

• [ ] Bugfix (non-breaking change which fixes an issue)
• [X] New feature (non-breaking change which adds functionality)
• [ ] Breaking change (fix or feature that would cause existing functionality to not work as expected)

Checklist

Put an x in the boxes that apply.

• [ ] I have read the CONTRIBUTING doc
• [ ] I am making a pull request against the develop branch (left side). Also you should start your branch off our develop.
• [ ] Lint and unit tests pass locally with my changes
• [ ] I have added tests that prove my fix is effective or that my feature works

Further comments

n/a