1. Create biennial appointments
The President shall, during the first and third years after a year in which there is a presidential election, nominate, and by and with the advice and consent of the Senate, appoint one justice of the Supreme Court.
2. Lock in 18-year terms for future justices; exempt the current justices out of the statute
If there are more than nine justices on the Supreme Court after a newly appointed justice is sworn into office – i.e., 18 years after the bill is enacted – the justice who has served on the Supreme Court for the longest period of time shall be deemed a justice retired from regular active service.
No justice appointed before the date of enactment shall be required to retire, so for a time, the Supreme Court may comprise more than nine justices. (For how long? See this.)
3. Create the role of “senior justice”
Any retired justice shall be designated as a “senior justice” and may continue to perform judicial duties as s/he is willing and able to undertake on any federal court, unless that justice has been certified as disabled.
4. Describe a senior justice’s return to the court
When there is a vacancy on the Supreme Court due to the death, disability certification or removal of a justice, the retired justice who became senior justice first among the senior justices shall be assigned to serve on the Supreme Court until an appointment is made under section 1. If there is more than one vacancy, senior justices will be seated on the Court in the order in which they first assumed senior status[1].
[1] For example, Justice Souter, who retired in 2009, would return to the Court before Justice Kennedy, who retired in 2018.