If you don't mind I start a new thread here. The unsigned infinite precision integer is different from the base type unsigned int, which is actually a modular integer with modulus 2^n. Therefore two integer derived classes are needed: unsigned_integer and modular_integer. The unsigned_integer is an infinite precision integer which can only be positive or zero. The negate() of a non-zero unsigned_integer will always throw an exception. A subtraction which results in a negative value will do the same; therefore in my opinion there is no fundamental problem with this, as negation is subtraction from zero. The modular_integer has a static method static void set_modulus( const integer & ). When the modulus is not set, it is zero, in that case the modular_integer is identical to integer. Users that like an unsigned integer with a negate() that always works, will have to use a modular_integer and set its modulus to a positive value. In the document I will specify unsigned_integer and modular_integer, and thus implementations can provide them. Regards, Maarten.