User:Lord Farin/Sandbox/Proof Rules

Refactoring of Proof Rules
The pages in Category:Proof Rules are currently focused on PropLog. As I cover more ground in PredLog, most of the proof rules transfer.

Not all systems have equivalent rules of inference and derived rules.

To accommodate for further coverage of these subjects we ought to design these pages in a way that we can easily add the references to new proof systems having these rules.

This includes the proof of being a derived rule if necessary. Those pages will look like Deduction Theorem and will be interlinked in a standard way.

Applications will mostly lie in deriving stuff like Completeness Theorems, but once we get to deeper parts of proof theory it is going to be very convenient to have this solid foundation.

Considerations
The current state of affairs is reminiscent to the conflation of first order model theory and formal semantics. In a similar manner the generic and specific are intertwined and need to be extracted. In this case, the specific being the coverage of PropLog.

Aim is to restructure the definition/exposition, and not affect the content and/or the proofs based on that. Just give them a more specific foundation in PropLog, or PredLog as applicable.

There will be references in multiple ways:
 * The PR page will link to the systems having these rules, and will link to the proofs of these statements where it concerns derived rules
 * The systems will link to the PR page for the standard rules (as done now)
 * The systems will link to the derived rules in a separate section for derived rules
 * The proofs will by definition link to PR and PS, but aim for doing so in a standard manner

Exposition of relevant pages
Definitions:


 * Definition:Proof Rule (subpage of Definition:Natural Deduction)
 * Definition:Rule of Inference
 * Definition:Derived Rule

Lists and categories:


 * Definition:Natural Deduction
 * Definition:Elementary Valid Argument Form
 * Definition:Natural Deduction System
 * Category:Proof Rules

Decisions made

 * Definition:Proof Rule and Definition:Rule of Inference will merge.
 * The PR pages will be refactored to generalise them from Definition:Natural Deduction to a general proof system
 * There will be a clear distinction made between a standard rule and a derived rule. As in "the following PS have this as a rule of inference: list. the following PS have this as a derived rule: list (link to proof)".
 * There will be a separate page/separate pages listing out the specific PRs for the various types of PropLog. These will be appropriately referenced.
 * Main focus of this project will be to come up with a crisp and clear presentation of these concepts and their occurrences for various types of logic and proof systems.
 * There will remain a separate branch for coverage of PropLog/PredLog on . Just like we have a "canonical" Language of PropLog and PredLog.
 * Proofs of equivalence of the various proof systems will be out of scope of this project to keep it manageable.
 * PR and RoI will remain as interchangeable names on due to prohibitive and unwarranted refactoring costs associated.
 * There will be a category Category:Derived Rules of Inference or Category:Derived Proof Rules or just Category:Derived Rules to contain the derived rules proofs.
 * Definition:Natural Deduction will be phrased as a proof system, with reference to a Definition:Gentzen Proof System. However, due to the presentation in e.g. Huth-Ryan being informal, it will be necessary to give a warning about the informality. Obviously, the informality does not influence the everyday applicability of the system on, and it is exactly because of this informality that it is easily used and properly readable.