A liquidator may close up to a certain fixed percentage (i.e. close factor) of any individual outstanding borrow of the underwater account. Unlike in v1, liquidators must interact with each aToken contract in which they wish to repay a borrow and seize another asset as collateral. When collateral is seized, the liquidator is transferred aTokens, which they may redeem the same as if they had supplied the asset themselves. Users must approve each aToken contract before calling liquidate (i.e. on the borrowed asset which they are repaying), as they are transferring funds into the contract.