We doubt that Brian is a rhino. There is a very good chance that Sandra left the football. It is improbable that Julius is a frog. Chances are slight that if 'Sandra left the football' or 'Brian is a rhino' or both then Bill got the milk there. It is probably not the case that if 'Julius is a frog' or 'Sandra left the football' or both then Greg is a swan. It is highly unlikely that if 'Julius is a frog and Brian is a rhino' then Jeff went to the bedroom.
It is probably not the case that either 'Greg is a swan' or 'Julius is a frog' but not both.
It is probably not the case that either 'Greg is a swan' or 'Julius is a frog' but not both.
It is almost certain that either 'Greg is a swan' or 'Julius is a frog' 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
  0.2::factA.
  0.8::factB.
  0.1::factC.
  %hop1
  0.1::factX:-or(factB,factA).
  0.25::factY:-or(factC,factB).
  0.05::factZ:-and(factC,factA).

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

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