Works exactly like Redeem, but instead allows you specify the amount of underlying tokens you'd like back (saving you from having to calculate/use the mToken exchangeRate)
Borrows a specific amount of assets from the protocol - only allowed if you have supplied (minted) collateral and called enterMarket with it, and you have sufficient liquidity to borrow the requested asset
Get the balance of an mToken holder denominated in the underlying asset instead of the mToken balance (accruing interest and calculating the balance from the exchange rate)