Chances are slight that Lily is a swan. It is highly likely that Brian is a frog. It is impossible that Julius is yellow. We believe that if either 'Julius is yellow' or 'Brian is a frog' but not both then Greg is white. There is little chance that if 'Julius is yellow' or 'Lily is a swan' or both then John discarded the apple. We doubt that if 'Lily is a swan and Julius is yellow' then Mary moved to the office.
There is a better than even chance that either 'Lily is a swan' or 'Greg is white' but not both.
There is a better than even chance that either 'Lily is a swan' or 'Greg is white' but not both.
It is highly unlikely that either 'Lily is a swan' or 'Greg is white' 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.
  0.9::factB.
  0.0::factC.
  %hop1
  0.75::factX:-xor(factC,factB).
  0.1::factY:-or(factC,factA).
  0.2::factZ:-and(factA,factC).

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

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