# One-Sided Liveness

> A design rule that a process's absence proves it is dead while its presence proves nothing, so liveness is derived once, from the witness first and from a generous window only where the witness cannot decide.

Record: `architecture:one-sided-liveness`
Kind: principle
Layer: [Execution Core](https://banes-lab.com/records/layer/execution-core.md)
Severity: recommended
Scope: process, liveness
Canonical: https://banes-lab.com/ontology#architecture-one-sided-liveness

Listed in [Architecture principles](https://banes-lab.com/api/records/architecture.md), after [Read-Time Join](https://banes-lab.com/records/architecture/read-time-join.md) and before [Reversible Channel Encoding](https://banes-lab.com/records/architecture/reversible-channel-encoding.md).

## Repair

- Refactored by: Derive Liveness Once, Witness First, Window Second
- Detected by: two consumers of one liveness question reaching different answers
- Violated by: treating a present process as alive, or computing liveness separately in each consumer
- Measured by: liveness derivations outside the single one
- Enforced by: coordination review

## Requires

- [Liveness Witness](https://banes-lab.com/records/lexicon/liveness-witness.md)

## Reinforces

- [Determinism](https://banes-lab.com/records/architecture/determinism.md)

## Enables

- [Shared Invocation](https://banes-lab.com/records/lexicon/shared-invocation.md)

## Severity

- [recommended](https://banes-lab.com/records/vocabulary/severity-recommended.md)

## Category

- [Coordination Surfaces](https://banes-lab.com/records/architecture-category/coordination-surfaces.md)

## Linked from

- [Correctness / Determinism / Verification](https://banes-lab.com/ontology/principles/architecture-category-correctness-determinism-verification.md)
- [Coordination Surfaces](https://banes-lab.com/ontology/lexicon/lexicon-category-coordination-surfaces.md)
- [Severity levels](https://banes-lab.com/ontology/schema/the-vocabulary-severity.md)

## Evidence in the code

- [models/invocation.model.md](https://banes-lab.com/source/coordination/models/invocation.model.md.md)