Training-free Verifiable Process Reward for LLM Reinforcement Finetuning

This thesis project, started in October 2025, develops a training-free verifiable process reward for reinforcement finetuning of large language models. The implementation is available in the verl repository.

Approach

• Forcing LLMs generate natural-language reasoning steps in Horn clause form, such as \(p \land q \to r\), so the reasoning process can be segmented into semantically meaningful steps.
• A theorem prover or solver acts as a verifier and checks each reasoning step.
• A teacher LLM formalizes natural-language reasoning into verifier-compatible expressions.
• A GRPO-like advantage normalization method estimates critic-free values for process rewards.

Evaluation

Experiments use logical and mathematical question-answering datasets. The system is evaluated by comparing reasoning-model accuracy before and after reinforcement finetuning with the proposed process reward.