This program is used by the internal auto-bignum conversion. It can be used to explicitly type integers that are too big to be INT_TYPE. Best is however to not use this program unless you really know what you are doing.
Due to the auto-bignum conversion, all integers can be treated as Gmp.mpz objects insofar as that they can be indexed with the functions in the Gmp.mpz class. For instance, to calculate the greatest common divisor between
85, you can do
51->gcd(85). In other words, all the functions in Gmp.mpz are also available here.