<SYSTEM_TASK:>
Solve the following problem using Python, implementing the functions described below, one line at a time
<END_TASK>
<USER_TASK:>
Description:
 def combine(self, patch):
 """Add `patch.plist` to `self.plist`."""

        exclusive = set(["config", "default", "mandatory", "presence",
                     "min-elements", "max-elements"])
        kws = set([s.keyword for s in self.plist]) & exclusive
        add = [n for n in patch.plist if n.keyword not in kws]
        self.plist.extend(add)