The previous system followed Jim Moores' description, which turns out to not be how KRoC does it, and different enough that lots of existing occam code was failing.
The new system makes two changes. First, if there is only one suitable operator, given the types (taking Infer to be a wild-card) then it uses that operator, and can usually settle any remaining Infers. Second, it uses the type context to narrow down the operators to only those that have a matching return type. These changes seem enough to compile a lot of the trickier types.
