Deriving a descriptor from a wildcard-parameterized type (Predicate<? super Number>), in the absence of an explicit lambda, uses the use-site bound by not any declaration-site bounds. This is an unnecessary limitation.

Also, a wildcard-parameterized type has a descriptor only if its non-wildcard counterpart is a well-formed type (type arguments are within their bounds). But we don't have a way to test for well-formedness of a non-proper type during inference. So the derivation process needs to guarantee that the type will be well-formed, for all ivar instantiations.