direct_proof

Construct direct proofs in Lean 4 by applying definitions and inference rules.

1|Updated Mar 14, 2026
One-click install
npx skills add https://github.com/bneb/perqed --skill direct-proof-bneb
Or copy as Structured Prompt for Agent
Please help me install this Agent Skill.
Skill: direct_proof
Source: https://github.com/bneb/perqed/tree/main/.agents/skills/direct_proof
Command: npx skills add https://github.com/bneb/perqed --skill direct-proof-bneb

SYSTEM DOCUMENTATION & REQUIREMENTS

What problem does it solve?

Direct proof guides learners and practitioners to derive conclusions from hypotheses without resorting to case splits or contradiction, streamlining formal reasoning in Lean.

Core Features & Use Cases

  • Clear blueprint for constructing forward proofs in Lean 4 using intro, apply, exact, and calc.
  • Guidance on handling universal and existential goals, including explicit witnesses where needed.
  • Practical templates and examples for building concise, readable proof scripts in mathematical contexts.

Quick Start

Prove a simple implication by assuming the antecedent and applying established lemmas to derive the consequent.

Frequently Asked Questions about direct_proof

High-intent search queries and answers about installing and using this skill.

FAQPage Schema
How do I write a direct proof in Lean 4 without using contradiction or case splits?

A direct proof in Lean 4 assumes the antecedent with intro and systematically applies definitions, lemmas, and inference rules via apply or exact to forward-reason toward the consequent without contradiction.

What is the best way to handle existential goals in Lean 4 mathlib4?

Handling existential goals in Lean 4 mathlib4 requires providing an explicit witness, then systematically applying definitions and basic tactics like apply or exact to close the remaining proof leaves.

Can I use calc blocks for forward reasoning in Lean 4 direct proofs?

Yes, calc blocks provide a structured proof environment for forward reasoning in Lean 4, allowing you to systematically chain definitions and lemmas to derive a conclusion from hypotheses.

Do I need to provide explicit witnesses for universal statements in Lean 4?

No, universal statements in Lean 4 are handled by introducing variables with intro, whereas existential goals require explicit witnesses to construct the derivation and close the proof.

Why does my direct proof stall when applying lemmas to hypotheses in Lean 4?

Direct proofs stall in Lean 4 when the structured proof environment lacks proper forward reasoning; systematically applying definitions and lemmas via intro, apply, exact, and calc resolves remaining proof leaves.

When should I avoid direct proofs and use other tactics in Lean 4?

Avoid direct proofs in Lean 4 when the derivation cannot be constructed by purely forward reasoning from hypotheses, requiring case splits or contradiction tactics to close the goal instead.