I note the following on [cppreference's article for `std::mersenne_twister_engine`](https://en.cppreference.com/w/cpp/numeric/random/mersenne_twister_engine) (e.g. `std::mt19937`):

> 
> The 10000th consecutive invocation of a default-constructed `std::mt19937` is required to produce the value `4123659995`.
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> The 10000th consecutive invocation of a default-constructed `std::mt19937_64` is required to produce the value `9981545732273789042`.
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> 
> 

Assuming that this interpretation of the standard is accurate, what's the deal? Why do these guarantees exist? Isn't this *non-random*?