Interfaces, Contracts & Hidden Implementation

Primes about separating an observable contract from the implementation behind it: abstract data types and the open-closed principle hide internals behind a stable surface, while confused deputy, observable-surface-becomes-contract, and refactoring examine how authority, dependency, or structure shift once that boundary is in place.

22 primes in this family — primes that sit near one another in abstraction space (k-means over structural-signature embeddings). Each is shown with its short description.

• Abstract Data Type — Specify a component by its externally observable behaviour while suppressing its implementation, so any conforming implementation is interchangeable behind the contract.
• Adjacency Pair — A typed first move that conditions a second and makes its absence noticeable.
• Aspectual Individual — Treating a single underlying entity, under a fixed role or aspect, as a distinct derived bearer of properties with its own narrower existence conditions.
• Client Server Model — An asymmetric request-response relation in which one party holds a capability and many others initiate to consume it.
• Confused Deputy — A privileged intermediary acts on its own authority while the intent originated with an outsider who lacks it, so authority is borrowed without intent being tracked.
• Input/output — The typed exchange boundary through which a system receives state-changing signals or data and emits signals, data, actions or effects to its environment.
• Interface Mismatch — Two systems that are locally workable fail to compose because what one exposes at their required exchange boundary does not satisfy what the other can accept, including the limiting case where the needed handoff surface is absent.
• Law of Conservation of Complexity — Every problem has an irreducible complexity floor that design can shift between parties or moments but cannot reduce below the floor.
• Message Passing — Autonomous holders of private state interact only through discrete addressed messages over intermediating channels.
• Multiple realizability — The same higher-level role or property can be instantiated by materially different lower-level structures.
• Negative Case Analysis — Deliberately hunt the cases that would overturn your account, then revise or scope it.
• Observable Surface Becomes Contract — Every observable behaviour, exposed to enough observers over enough time, becomes a binding dependency regardless of the nominal contract.
• Open-Closed Principle — Harden a stable kernel against modification and route all change through an open extension surface.
• Operationalization — A specification of what is wanted is mechanically lowered into an executable how, under a correctness contract relating the two.
• Permission-Gated Hold — An otherwise ready flow remains blocked until an external authority emits a required authorization, making completion depend on administrative release rather than on the flow's own movement or production capacity.
• Provenance Laundering — Provenance laundering routes an item through successive intermediaries so its disfavored or unverifiable origin becomes harder to recover while inherited channel authority is mistaken for independent authentication.
• Refactoring — Change internal structure while preserving observable behavior.
• Revocation Closure — An issuer retains a bounded-time path to invalidate every active manifestation and downstream derivative of a grant, so withdrawal reaches the grant's actual effect set rather than only the issuer's registry.
• Role Fluidity — Role fluidity allows the same occupant to move among positions that a rigid system assigns to separate actors, so producer/consumer, leader/follower, or requester/provider functions can alternate without changing occupant identity.
• Supersession — A successor explicitly displaces a predecessor in a role, which the predecessor no longer fills going forward even while it persists for historical reference.
• Wizard Of Oz Prototyping — Validate a planned system cheaply by making its surface convincingly present while a hidden operator supplies the not-yet-built interior.
• Zero Knowledge Proof — Convince a verifier a claim is true while revealing nothing beyond its truth.