# invariant

> A claim that a property holds in every state the surface reaches.

Record: `vocabulary:predicate-type-invariant`
Kind: predicate-type
Canonical: https://banes-lab.com/ontology/schema#vocabulary-predicate-type-invariant

Listed in [Controlled vocabularies](https://banes-lab.com/api/records/vocabulary.md), after [unknown](https://banes-lab.com/records/vocabulary/verdict-unknown.md) and before [equivalence](https://banes-lab.com/records/vocabulary/predicate-type-equivalence.md).

## Predicate type of

- [functional-correctness](https://banes-lab.com/records/reasoning/test-surface-functional-correctness.md)
- [concurrency-correctness](https://banes-lab.com/records/reasoning/test-surface-concurrency-correctness.md)
- [consistency-correctness](https://banes-lab.com/records/reasoning/test-surface-consistency-correctness.md)
- [data-correctness](https://banes-lab.com/records/reasoning/test-surface-data-correctness.md)
- [numerical-correctness](https://banes-lab.com/records/reasoning/test-surface-numerical-correctness.md)
- [observability-correctness](https://banes-lab.com/records/reasoning/test-surface-observability-correctness.md)

## Linked from

- [The test surfaces](https://banes-lab.com/ontology/reasoning/the-test-surfaces.md)