> For the complete documentation index, see [llms.txt](https://docs.ionprotocol.io/llms.txt). Markdown versions of documentation pages are available by appending `.md` to page URLs; this page is available as [Markdown](https://docs.ionprotocol.io/devs/smart-contract-architecture/periphery.md).

# Periphery

- [IonInvariants](https://docs.ionprotocol.io/devs/smart-contract-architecture/periphery/ioninvariants.md)
- [IonLens](https://docs.ionprotocol.io/devs/smart-contract-architecture/periphery/ionlens.md)
- [IlkSlot0](https://docs.ionprotocol.io/devs/smart-contract-architecture/periphery/ilkslot0.md)
- [IonRegistry](https://docs.ionprotocol.io/devs/smart-contract-architecture/periphery/ionregistry.md)