There are (at least) two trapdoors. The first is that an operation on Rats which would produce a denominator which does not fit in a 64-bit unsigned integer wi

There are (at least) two trapdoors. The first is that an operation on Rats which would produce a denominator which does not fit in a 64-bit unsigned integer will produce a Num instead. (If you're okay with your denominators growing in an unbounded fashion, you can use the FatRat class instead.) The second "trapdoor" is that you can just explicitly work with Nums (ie C doubles). If your numeric literal has a exponent (eg 1e-15), it's automatically a Num. Or you can convert any Real numeric type to a Num by calling the .Num method on it.