510. Combat Damage Step
510.1. First, the active player announces how each attacking creature assigns its combat damage, then the defending player announces how each blocking creature assigns its combat damage. ...

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510.4. Fourth, the active player gets priority. Players may cast spells and activate abilities.

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511. End of Combat Step
511.1. First, all “at end of combat” abilities trigger and go on the stack. (See rule 603, “Handling Triggered Abilities.”)
511.2. Second, the active player gets priority. Players may cast spells and activate abilities.
511.3. As soon as the end of combat step ends, all creatures and planeswalkers are removed from combat. After the end of combat step ends, the combat phase is over and the postcombat main phase begins (see rule 505).