There is a very good chance that Mary went to the bedroom. It is almost certain that Brian is a lion. There is a very good chance that Greg is green. We doubt that if 'Mary went to the bedroom' or 'Brian is a lion' or both then Lily is a rhino. It is impossible that if 'Brian is a lion and Greg is green' then John left the football. It is probable that if either 'Greg is green' or 'Brian is a lion' but not both then Sandra took the football.
It is unlikely that either 'Lily is a rhino' or 'Greg is green' but not both.
It is probable that either 'Lily is a rhino' or 'Greg is green' but not both.
It is unlikely that either 'Lily is a rhino' or 'Greg is green' but not both.

  and(A,B) :- A,B.
  or(A,B) :- A;B.
  nand(A,B) :- not(and(A,B)).
  nor(A,B) :- not(or(A,B)).
  xor(A,B) :- or(A,B), nand(A,B).

  %hop0
  0.8::factA.
  0.95::factB.
  0.8::factC.
  %hop1
  0.2::factX:-or(factA,factB).
  0.0::factY:-and(factB,factC).
  0.7::factZ:-xor(factC,factB).

  %hop2
  conclusion:-xor(factX,factC).

  query(conclusion).
  
Either 'Lily is a rhino' or 'Greg is green' but not both.