+ | (C.Sort C.Set, C.Sort C.CProp) when need_dummy -> true
+ | (C.Sort C.CProp, C.Sort C.Set) when need_dummy -> true
+ | (C.Sort C.CProp, C.Sort C.CProp) when need_dummy -> true
+ | ((C.Sort C.Set, C.Sort C.Type) | (C.Sort C.CProp, C.Sort C.Type))
+ when need_dummy ->