1.   Another possible scenario would be that issuers must buy back existing notes from investors.

2.   Commonly, the issuers buy a mix of ordinary Treasury securities and special zero-interest or very-low-interest Treasury paper issued specifically for escrow accounts.

3.   The non-callable bonds include a sinking-fund provision, which enables the issuer to buy back the bonds early.

4.   To comply with that law, issuers typically buy a mix of ordinary Treasury securities in the open market or special securities, called slugs, from the Treasury.