Dear all,
to "close" this issue:
can CPF/CeTA do "split" for relative termination?
yes it can - and matchbox is using it now.
René explained to me that a design principle in CeTA is (I am paraphrasing) "everything is relative" : a TRS always is a pair (R,S) of sets of (strict and weak) rules, and where this does not make sense, the union R+S is considered.
- Johannes.