Integer without restrictions

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On Sunday, 15 March 2020 at 19:03:54 UTC, Paul Backus wrote:
> On Sunday, 15 March 2020 at 19:02:00 UTC, ... wrote:
>> How to create an integer without restrictions of size? Do I 
>> need to create a new class or there is a type of integer that 
>> doesn't have any restrictions in size?
>
> http://dpldocs.info/experimental-docs/std.bigint.html

And if I need to create very large value, how to use GMP library 
(It isn't described in that post)?