[API reference](https://evolu.dev/docs/api-reference) › [@evolu/common](https://evolu.dev/docs/api-reference/common) › [Lookup](https://evolu.dev/docs/api-reference/common/Lookup) › LookupOption

Defined in: [packages/common/src/Lookup.ts:42](https://github.com/evoluhq/evolu/blob/037c390af081e9944d616ff298a729515c5c5ab7/packages/common/src/Lookup.ts#L42)

Optional [Lookup](https://evolu.dev/docs/api-reference/common/Lookup/type-aliases/Lookup).

## Extended by

- [`CreateRefCountByKeyOptions`](https://evolu.dev/docs/api-reference/common/RefCount/interfaces/CreateRefCountByKeyOptions)
- [`SharedResourceByKeyOptions`](https://evolu.dev/docs/api-reference/common/Resource/interfaces/SharedResourceByKeyOptions)
- [`CreateSemaphoreByKeyOptions`](https://evolu.dev/docs/api-reference/common/Task/interfaces/CreateSemaphoreByKeyOptions)
- [`CreateMutexByKeyOptions`](https://evolu.dev/docs/api-reference/common/Task/interfaces/CreateMutexByKeyOptions)

## Properties

<a id="lookup"></a>

### lookup?

```ts
readonly optional lookup?: Lookup<K, L>;
```

Defined in: [packages/common/src/Lookup.ts:44](https://github.com/evoluhq/evolu/blob/037c390af081e9944d616ff298a729515c5c5ab7/packages/common/src/Lookup.ts#L44)

Derives the lookup key used for logical equality.