It is highly likely that Greg is white. We doubt that Julius is a swan. It is highly unlikely that John went to the hallway. It is probable that if either 'Julius is a swan' or 'Greg is white' but not both then Gertrude is a sheep. It is probably the case that if 'John went to the hallway' or 'Greg is white' or both then Lily is a rhino. It is likely that if 'Julius is a swan' or 'Greg is white' or both then Mary discarded the apple.
We doubt that either 'Greg is white' or 'Julius is a swan' but not both.
We believe that either 'Greg is white' or 'Julius is a swan' but not both.
We doubt that either 'Greg is white' or 'Julius 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
  0.9::factA.
  0.2::factB.
  0.05::factC.
  %hop1
  0.7::factX:-xor(factB,factA).
  0.7::factY:-or(factC,factA).
  0.7::factZ:-or(factB,factA).

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

  query(conclusion).
  
Either 'Greg is white' or 'Julius is a swan' but not both.