Rule 104.6 · Ending the Game
One card (Karn Liberated) restarts the game. All players still in the game when it restarts then immediately begin a new game. See rule 727, “Restarting the Game.”
Ask the judge Pro
The life counter has an AI judge that answers your play citing the exact rules. It is part of Gatewatch Pro; the rules, Oracle text and rulings stay free.