CB-RES-0009: extensive form is the lingua franca

Two questions from the maintainer — is there a game-theory mapping to
Ludii's language, and is that language formal enough to derive one from.
Yes, no, and the no does not matter.

The mapping is proven, not to be invented: "The Ludii Game Description
Language is Universal" shows the language can represent an equivalent game
for any finite, non-deterministic, imperfect-information game, extending
earlier work limited to finite deterministic fully-observable
extensive-form games. EFG is also OpenSpiel's object, so the same
formalism connects description to analysis: Ludii -> EFG <- OpenSpiel.

Ludii's syntax is formal and unusually so — a class grammar derived
automatically from its source. Its semantics are its Java: a ludeme means
what its class does, and Ludii effectively makes Java the game description
language. So there is no independent calculus to extract. The formality
lives in the universality RESULT, not in a definition of meaning. GDL has
the semantics and pays for it in speed — six times on Gomoku, twenty on
Amazons and Hex, over two hundred on Chess.

Conclusion: do not derive a language from Ludii; target the EFG directly.

And we are closer than the tracks assumed. The journal is the history,
Outcome is the payoff, legal_commands gives the actions — and
project(Viewer::Player(seat)) IS the information partition, built so a
player is not shown another's hand and unremarked as exactly the machinery
imperfect information needs.

Three gaps: chance is folded into a seed so a game is one realisation
rather than a game with chance nodes; perfect recall is unasserted, which
CFR and exploitability both assume; and commit/reveal is the standard EFG
encoding of simultaneity but is never stated as such. Perfect recall is
checkable from the journal today and is now Track B's first task — if it
fails, every equilibrium concept we might quote is unsound here.

Also re-vendored the catalog twice: ground-game added H2 — scoped problem
stress, applying End Stress by personal/bond/global scope instead of flat
to everyone, which is a direct response to our reading that H1's tax
scales with the Problems while its intended effect does not.

Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>

specs/Positioning.md

@@ -153,11 +153,32 @@ everything else, because a Nash equilibrium quoted without its assumptions
 is exactly the wrong-subject error in mathematical dress
 ([`Taxonomy.md`](Taxonomy.md) §2.2).
 
-**But the first task is not to build it.** It is to answer one question:
-**is exploitability meaningful for a co-operative game with a shared
-threshold?** If yes, Track B is mostly integration with
-[OpenSpiel](../simulators/openspiel.md). If no, that is a real research
-finding and the reason a specialised agent is needed at all.
+**But the first task is not to build it**, and the survey narrowed it
+twice more ([`../research/CB-RES-0009-extensive-form-is-the-lingua-franca.md`](../research/CB-RES-0009-extensive-form-is-the-lingua-franca.md)).
+
+**The formal object is the extensive-form game**, proven expressive enough
+by Ludii's universality result and consumed directly by OpenSpiel — so
+"Ludii → EFG ← OpenSpiel" is the whole mapping, and there is nothing to
+invent.
+
+**And we already have most of an EFG**: the journal is the history, the
+payoff is `Outcome`, and **`project(Viewer::Player(seat))` is the
+information partition** — built so a player is not shown another's hand,
+and unremarked as the machinery imperfect information needs.
+
+**Three gaps, one checkable today:**
+
+1. **chance is folded into a seed**, so a clay-borg game is one
+   realisation rather than a game with chance nodes;
+2. **perfect recall is unasserted** — CFR and exploitability assume a
+   player remembers their own past actions and observations, and nobody
+   has checked whether our projection sequence does;
+3. simultaneity is encoded by commit/reveal but never *stated* as the
+   standard EFG encoding.
+
+**Track B's first task is (2)**, because it is small, checkable from the
+journal, and if it fails every equilibrium concept we might quote is
+unsound here. That is a better opening move than a build.
 
 ### Track C — assimilated knowledge about why games work