Updated repository for the ILF system, reduced to natural language presentation of Prover 9 proofs

ILF (Integrated Logic Functions) was a system for integrating various automated theorem provers, running distributed in a local network. ILF had an interactive theorem prover, called ProofPad, for block structured proofs with a graphical user interface. ILF was capable to automatically restructure proofs from various provers into natural language and to restructure them.

The ILF system was developed between 1988 and 1998 at the Humboldt University in Berlin/Germany. It's development was supported in part by the Deutsche Forschungsgemeinschaft within the DFG Schwerpunkt "Deduktion". Key developers of the system were Ingo Dahn (Project Leader), Juergen Gehne, Thomas Honigmann, Andreas Wolf, Thomas Baar, Lutz Walther, Thomas Baar, Oliver Becker and many others.

In response to a user request in 2016, Ingo Dahn revived the capability of the ILF system to generate English presentations of proofs generated by the Prover 9 automated theorem prover, a successor of the Bill McCune's Otter prover which was integrated in the original ILF system. This repository provides the actualized ILF sources to solve this problem.

As a first step, ILF parses the proof as printed by the automated prover and translates it into a format that can be read by Prolog logic programming systems. Then this is connected with information about the axiom system used for the proof. In the next step, it is transformed into a block structured proof - sequence of proof steps, each justified from previous proof steps either by a rule of inference or by a subproof.

Then this block structured proof is simplified and restructured, using a set of ILF's proof transformation tools. A natural language LaTeX presentation of this proof is generated using a variable set of templates.

ILF requires an installation of the Eclipe Constraint Logic Programming System and of Perl as well as the files in this repository. The file ilf_state.pl need to be adapted for the local installation: Adapt the paths prologhome to Eclipse prolog, ilfhome to the root of this repository, userilfhome can be set to the same value and default_proof_file for the LaTeX file to be generated.

As a first step, the Prover 9 proof needs to be converted into a Prolog format as preparation/JoaoProof4.opf.tmp.1. The tool to do this conversion will hopefully be contributed to this repository by its author.

The following step requires an additional file, like preparation/JoaoProof4.axn that describes the axiom system that was used in the proof. The Eclipse Prolog program preparation/convert.pl connects both files and produces a file like preparation/JoaoProof4.out. Copy this file to the root folder of this repository.

In order to transform this file into a block structured proof and simplify it, compile the Eclipse Prolog file aa_ilfmnu.pl and call start in the module ilfmnu (call(start)@ilfmnu). A listing of the prolog structure representing the proof to be Texed can be obtained by the Prolog command call(lising(proof/3))@situation.

The final step produces the LaTeX file with the Prolog command prooftex. It is normal that this command fails.

The files in this repository have been adapted from the original ILF system as little as possible and have not been systematically cleaned up. In fact, not all files will be needed.