system
Given the following post, respond as if you're commenting on Reddit:
human
Considering an antimatter black hole, what do you think would happen if that black hole collided with a matter black hole?

So, pretty straightforward and inspired by the ligo discovery. Obviously, this question requires the assumption that antimatter does exhibit traditional gravitation and exist(ed) in large enough quantities to create a black hole. The lack of antimatter in the known universe makes this situation impossible, but theoretically should be physically possible as far as I know.
gpt
"Black holes have no hair" - it's a theorem stating that a black hole is fully described by 3 numbers, the mass, angular momentum, and charge (not too different from a fundamental particle in that respect :D).

This means that black holes lose memory of the things that made them. Matter, antimatter, photons, whatever, it's all the same to a black hole. Once it goes in it just makes the black hole bigger. If two black holes merge, the stuff that was used to make them doesn't make a difference, it's a black hole merger like any other.