Argon

Argon is a knowledge-representation language and graph database. You declare an ontology — concepts, the relations between them, and the rules that derive new facts — and Argon compiles it to a content-addressed artifact you can query, reason over, mutate, and serve.

This book is the surface specification: the syntax and meaning of an Argon program — the precise reference, chapter by chapter, in the technical specification and its appendices.

For a guided, motivated tour of the whole language, read The Argon Book, the teaching narrative (spec/book/). To watch real packages compile and run, see Argon by Example (examples/).

Two companion sources of truth sit beside this book:

• The Lean 4 mechanization (spec/lean/) is canonical for the substrate — the type system, reasoning semantics, and decidability results. Where the Lean and this book disagree on something the Lean covers, the Lean wins; the book is the bug.
• RFDs (Part II) record design decisions and their rationale. They are history, not normative spec.

Each chapter leads with a grammar fragment and a worked example before the prose. Cross-references are named links; each names the chapter or section it points to.