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evo-lean4-recursive-sequence-inequality-proof

Provides utilities and guidance for constructing Lean 4 proofs involving recursive sequences and geometric sum inequalities. Covers reading existing Lean template files, crafting induction-based proofs with closed-form intermediate lemmas, and using math2001 textbook tactics (simple_induction, numbers, addarith, extra, rel) plus Mathlib4 tactics (norm_num, linarith, positivity, ring, field_simp) to handle arithmetic over rationals with powers of 2.

tasks-evolved/lean4-proof/environment/skills/evo-lean4-recursive-sequence-inequality-proof/SKILL.md

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# Lean 4 Recursive Sequence Inequality Proof Skill

## Overview

This skill solves problems of the form: given a recursively defined sequence
`S : ℕ → ℚ` (e.g., geometric partial sums), prove an inequality like `S n ≤ C`
for all natural numbers.

## Key Strategy: Closed-Form Lemma + Inequality

The recommended proof approach has two parts:

1. **Prove a closed-form lemma**: Show `S n = 2 - 1 / 2^n` by induction
2. **Derive the inequality**: Since `1/2^n ≥ 0`, we get `S n = 2 - 1/2^n ≤ 2`