I don't see have conversions in only a single direction as a coherent enough set of functionality that it makes sense to support in IMP. So I think if we drop conversion in one direction, we should drop it in both, otherwise, if anyone actually uses it, we will have to revisit this question in the future. The code in question is nicely self-contained, so it is pretty straight forward for it to be dropped into anywhere that it is actually needed (so if there is code that we don't know about that uses it, it could be very quickly patched more or less by pasting the code we removed from IMP into it in much less time than has already been spent discussing it :-).