So there is a process x that is well known and has an expired patent. The original patent does not specify what materials exactly can this process be used on. Basically,
(whatever) -> x -> (anything else)
There is an active patent (US123) for the transformation of materials (1) into (2) that specifies a process that looks like:
(1) -> a -> x -> b -> c -> (2).
This is a first instance where x is used on (1).
QUESTION: Can you register a patent that describes a process like this:
(1) -> x -> y -> z -> (2),
while US123 is still active?
Sorry for the somewhat confusing language, I tried to make this as broad as possible so that this question can be referred to by other people