[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:32](https://github.com/evoluhq/evolu/blob/e7144e2bbe9069362b62dec1b64a8aa922b8f1b0/packages/common/src/Lookup.ts#L32)

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:34](https://github.com/evoluhq/evolu/blob/e7144e2bbe9069362b62dec1b64a8aa922b8f1b0/packages/common/src/Lookup.ts#L34)

Derives the lookup key used for logical equality.