There is little chance that Greg is a rhino. There is a very good chance that Emily is a wolf. It is highly unlikely that Mary went to the hallway. It is highly likely that if either 'Greg is a rhino' or 'Mary went to the hallway' but not both then Sandra dropped the milk. It is improbable that if 'Greg is a rhino' or 'Emily is a wolf' or both then Brian is a swan. It is probably not the case that if 'Mary went to the hallway' or 'Emily is a wolf' or both then John took the apple.
It is probably not the case that either 'Emily is a wolf' or 'Mary went to the hallway' but not both.
We believe that either 'Emily is a wolf' or 'Mary went to the hallway' but not both.
It is probably not the case that either 'Emily is a wolf' or 'Mary went to the hallway' 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
  0.1::factA.
  0.8::factB.
  0.05::factC.
  %hop1
  0.9::factX:-xor(factA,factC).
  0.1::factY:-or(factA,factB).
  0.25::factZ:-or(factC,factB).

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

  query(conclusion).
  
Either 'Emily is a wolf' or 'Mary went to the hallway' but not both.