Wu-Decimal uses exact rationals (they aren't base 10 floats). Division works according to normal Lisp semantics, since the CL ratio type is used for arithmetic. Let's say you divide something by 3 and now you have infinitely repeating digits: then it is no longer in set D, and Wu-Decimal no longer considers it to be of decimal type. Instead, it is treated as a fraction, again per standard CL semantics. The "Printing" example tries to clarify this (notice that 1/2 prints as '0.5' but 1/3 remains '1/3').