The redeem function converts a specified quantity of sTokens into the underlying asset, and returns them to the user. The amount of underlying tokens received is equal to the quantity of sTokens redeemed, multiplied 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 redeem(uint redeemTokens) returns (uint)
SEther sToken = SEther(0x3FDB...);
require(sToken.redeem(7) == 0, "something went wrong");
const sToken = SErc20.at(0x3FDA...);