diff --git a/.org-ids.json b/.org-ids.json
index 12dafd9..a681e45 100644
--- a/.org-ids.json
+++ b/.org-ids.json
@@ -145,6 +145,7 @@
   "2f3a4b5c-6d7e-8f9a-0b1c-2d3e4f5a6b7c": "ideas/practical-powers-three-pronged.org",
   "a2811c83-b315-47fd-8ab8-25627c389d1a": "concepts/cl-modernization-timeline.org",
   "be9bccc7-5adf-4d0d-8ee4-8855892189bf": "concepts/neurosymbolic-loop-architectures.org",
+  "3e4f5a6b-7c8d-9e0f-1a2b-3c4d5e6f7a8b": "concepts/_index.org",
   "dddd52a7-adb8-470e-a459-614ade5f76af": "concepts/closing-the-lisp-gap.org",
   "85f963a7-a10f-45cc-ace6-6edfeefee762": "concepts/lisp-provers-and-rust-comparison.org",
   "e199190b-5eff-4a77-8aa5-b6c77647e316": "concepts/cl-modernization-initiative.org",
diff --git a/_index.org b/_index.org
index d63321c..c7b0c32 100644
--- a/_index.org
+++ b/_index.org
@@ -12,6 +12,14 @@ Personal knowledge base — projects, concepts, and meta-thinking.
 - [[id:1c3ec48b-446c-50d2-b53e-126a81f5143f][Passepartout]] — a verifiable personal intelligence: self-bootstrapping Lisp machine, gate-verified reasoning, social protocol. Architecture, staged roadmap, strategy, competitive analysis, compliance landscape.
 - [[id:1e5f6a7b-8c9d-0e1f-2a3b-4c5d6e7f8a9b][Flags]] — legal structures: entity types, jurisdictional analysis, asset protection, practical setup guides.
 
+** Concepts
+
+- [[id:85f963a7-a10f-45cc-ace6-6edfeefee762][Lisp, Provers, and vs Rust]] — Lisp vs Rust analysis, prover architecture, HOL bootstrap, comparison with Lean.
+- [[id:dddd52a7-adb8-470e-a459-614ade5f76af][Closing the Lisp Gap]] — performance and ecosystem gaps between Lisp and C/Rust, and how Passepartout closes them.
+- [[id:be9bccc7-5adf-4d0d-8ee4-8855892189bf][Neurosymbolic Loop Architectures]] — how neurosymbolic systems loop between symbolic reasoning and neural learning.
+- [[id:d2722576-fc9b-4bd3-bc2f-f5692b561b4e][Who Is Closest to Passepartout?]] — nearest-neighbor analysis of related projects.
+
 ** Concepts and meta-thinking
 
 - [[id:329a30cd-55fb-496d-a60b-91388c211bba][Ideas]] — cross-domain frameworks, reference material, and thinking tools.
+- [[id:3e4f5a6b-7c8d-9e0f-1a2b-3c4d5e6f7a8b][Concepts]] — in-depth analysis and comparative studies.
diff --git a/concepts/_index.org b/concepts/_index.org
new file mode 100644
index 0000000..426bda0
--- /dev/null
+++ b/concepts/_index.org
@@ -0,0 +1,10 @@
+:PROPERTIES:
+:CREATED:  [2026-05-24 Sun]
+:ID:       3e4f5a6b-7c8d-9e0f-1a2b-3c4d5e6f7a8b
+:END:
+#+title: Concepts
+#+filetags: :index:navigation:
+
+In-depth analysis and comparative studies of systems, languages, and architectures.
+
+{{< page-list >}}