There are lots of different philosophical views about what exactly maths is, how it works, how it should work, etc. But “simulation theory” isn’t really taken very seriously outside IT circles, so I’m not sure anyone has spent too much time thinking about what the implications would be for maths if it were true.
It’s important to bear in mind that maths is mostly made up of rigorously defined axiomatic systems and things that can be proved deductively from those axioms. The nature of our universe might have a big influence on which axiomatic systems and results we’re interested in, but it shouldn’t have any impact on what results are true in a given axiomatic system.
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