1% { p, r, not q }, { p, not q }, { q, not p, not r }
    2% p can succeed through not q, but not through r, since it would loop with no
    3% intervening negation. Similarly, r can succeed only if p succeeds through the
    4% first rule. Even with partial answer sets, not q will always be in any answer
    5% set with p or r.
    6
    7p :- not q.
    8q :- not p.
    9p :- r.
   10r :- p.
   11
   12_out :- r.
   13_out :- p.
   14_out :- q.
   15
   16#compute 0 { _out }.
   17%:- not _out.