f The landing coordinator
Receives the inspection result or a delivery-side question; returns an access offer or a survey request.
Inspect the current landing rules
| Incoming message | Authored response |
|---|
Geometry of Interaction / Field note 01
The Island
Reading Room
The books are on the boat.
The jetty is out of use.
Can two coordinators agree a delivery plan?
A tiny reading room needs shelves and books. At low tide, an inspection reports that the shore path is open. Follow the questions and replies between landing and delivery.
Follow the conversation
The seal is a bystander, not a decision-maker.Fig. 01 — Low tide
The project
Fit out one island reading room. Here, we model only the exchange that proposes a delivery plan.
The question
What happens when one coordinator’s answer becomes the other coordinator’s next input?
The mathematical move
Connect two signed interfaces, follow their feedback, then hide the internal conversation.
01 / Put the policies in conversation
A plan emerges one exchange at a time.
Start with a delivery request. The coordinators must ask for an access report before they can propose a route.
You supply the inspection result. The model does not invent a reply from the outside world.
Which reported access routes may be offered?
Can the delivery use a shore-path offer?
Selected here; supplied only when you click below.
Ochre marks the current input and output.
Each box applies one rule. Internal replies become the other box’s next input.
Ready / An external request
Ask for a delivery plan.
The project’s request is at C⁻. Take the first step to let the delivery coordinator respond.
The survey question has reached the outside world. Supply your selected report to start the next episode.
Changing a policy or report starts a fresh conversation. Choices stay in the page URL; reloading resets the steps.
The conversation so far
Explore a missing rule or a repeated internal cycle
A missing rule cannot answer an input. A cycle does keep answering, but repeats the same internal state without an exterior result. For the cycle, use shore allowed + fixed pallet + shore-only report.
g The delivery coordinator
Receives a project request or an access offer; returns a proposed plan or a question about landing.
Inspect the current delivery rules
| Incoming message | Authored response |
|---|
Reading the signs. A, B and C are interfaces, each with a + and a − side. In this example, + carries reports, offers and plans to the right; − carries questions to the left. The signs describe interface roles, not success and failure. A component can send a reply in either direction.
03 / Hide the conversation
What can the outside world see?
Composition follows the internal exchanges until a message exits. Hiding removes those middle messages from the resulting partial function.
g ∘ f : A⁺ ⊔ C⁻ ⇀ A⁻ ⊔ C⁺
One request produces a survey question. A separately supplied report may produce a proposed plan. These are two externally started episodes, not an automatically completed conversation.
| Exterior input | Exterior output of g ∘ f |
|---|
Computed from the current rules. “Undefined” means there is no entry in the partial function; the diagnostic distinguishes a missing rule from a witnessed cycle.
An identity copies each signed message through. Composition can be grouped either way. The model’s automated checks exercise identity and associativity on finite examples; those checks are not a general mathematical proof.
04 / Source → concept → construction → limit
The idea behind the island.
Symmetric feedback
The starting image is Abramsky’s two-box Geometry of Interaction diagram: a shared interface carries traffic in both directions.
Abramsky’s slide, p. 9 ↗Interaction & hiding
A’s and C’s signed ports stay outside. The B ports connect the components, and composition follows their interaction before hiding B.
GoI tutorial, p. 32 ↗A finite routing model
Each box is a typed partial function. The executable construction illustrates finite Int(Pfn, ⊔): disjoint-union interfaces with explicit missing routes and exact-state cycle detection.
GoI construction, pp. 28–33 ↗A plan, not a voyage
These are authored routing policies, not full game strategies. Legal plays, histories, payoffs and strategic incentives need more structure. No physical delivery, safe passage or human benefit is established here.
Game semantics, course notes ↗Want the earlier wiring experiment?
Its presets, port tests and token loops remain available as a separate comparison.