Chances are about even that Lily is a rhino. There is little chance that Daniel dropped the apple. It is impossible that Winona is a sheep. It is probably not the case that if 'Daniel dropped the apple and Lily is a rhino' then Greg is a swan. There is a very good chance that if either 'Lily is a rhino' or 'Winona is a sheep' but not both then Bernhard is a lion. There is a better than even chance that if 'Winona is a sheep' or 'Daniel dropped the apple' or both then John left the milk.
It is improbable that either 'Daniel dropped the apple' or 'Greg is a swan' but not both.
It is improbable that either 'Daniel dropped the apple' or 'Greg is a swan' but not both.
It is highly likely that either 'Daniel dropped the apple' or 'Greg is a swan' 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
  0.5::factA.
  0.1::factB.
  0.0::factC.
  %hop1
  0.25::factX:-and(factB,factA).
  0.8::factY:-xor(factA,factC).
  0.6::factZ:-or(factC,factB).

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

  query(conclusion).
  
Either 'Daniel dropped the apple' or 'Greg is a swan' but not both.