The redeem underlying function converts aTokens into a specified quantity of the underlying asset, and returns them to the user. The amount of aTokens redeemed is equal to the quantity of underlying tokens received, divided by the current Exchange Rate. The amount redeemed must be less than the user's Account Liquidity and the market's available liquidity.
SErc20 / SEther
function redeemUnderlying(uint redeemAmount) returns (uint)
msg.sender: The account to which redeemed funds shall be transferred.
redeemAmount: The amount of underlying to be redeemed.
SEther aToken = SEther(0x3FDB...);
require(aToken.redeemUnderlying(50) == 0, "something went wrong");
const aToken = SErc20.at(0x3FDA...);