* Enumerables: Improve gas cost of removal in `EnumerableSet` and `EnumerableMap`.
* Enumerables: Improve gas cost of lookup in `EnumerableSet` and `EnumerableMap`.
## Unreleased
## 4.1.0 (2021-04-29)
* `IERC20Metadata`: add a new extended interface that includes the optional `name()`, `symbol()` and `decimals()` functions. ([#2561](https://github.com/OpenZeppelin/openzeppelin-contracts/pull/2561))
* `ERC777`: make reception acquirement optional in `_mint`. ([#2552](https://github.com/OpenZeppelin/openzeppelin-contracts/pull/2552))