Cypher is Turing-Complete: A Formal Proof via 2-Counter Machine Simulation

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1. Verfasser: Halftermeyer, Pierre
Format: Preprint
Veröffentlicht: 2026
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author Halftermeyer, Pierre
author_facet Halftermeyer, Pierre
contents We prove that Cypher 25, the graph query language of Neo4j, is Turing-complete. The proof shows that a single RETURN statement using reduce(), CASE expressions, and list comprehensions can simulate any 2-counter machine (Minsky 1967). We address the bounded-step objection via two complementary resolutions and present a third graph-native simulation using quantified path patterns (QPP) with allReduce. All three constructions were verified on a live Neo4j Aura instance.
format Preprint
id arxiv_https___arxiv_org_abs_2605_18757
institution arXiv
publishDate 2026
record_format arxiv
spellingShingle Cypher is Turing-Complete: A Formal Proof via 2-Counter Machine Simulation
Halftermeyer, Pierre
Computational Complexity
Formal Languages and Automata Theory
Logic in Computer Science
Programming Languages
We prove that Cypher 25, the graph query language of Neo4j, is Turing-complete. The proof shows that a single RETURN statement using reduce(), CASE expressions, and list comprehensions can simulate any 2-counter machine (Minsky 1967). We address the bounded-step objection via two complementary resolutions and present a third graph-native simulation using quantified path patterns (QPP) with allReduce. All three constructions were verified on a live Neo4j Aura instance.
title Cypher is Turing-Complete: A Formal Proof via 2-Counter Machine Simulation
topic Computational Complexity
Formal Languages and Automata Theory
Logic in Computer Science
Programming Languages
url https://arxiv.org/abs/2605.18757