722—Redemption:  If debtor has prop subject to an SI, he can hold onto that prop if (1) the prop is exempt or has been abandoned by the trustee and (2) the full amount of the allowed secured claim is paid.  Again, the amount of the allowed secured claim is the amount of the debt or the value of the collateral, whichever is less—so that is what has to be paid to redeem.  Some cases have allowed installment redemption, while others have not.