It is likely that Julius is a swan. It is certain that John took the apple. It is unlikely that Greg is yellow. It is highly likely that if 'Greg is yellow and Julius is a swan' then Lily is gray. Chances are slight that if 'John took the apple' or 'Greg is yellow' or both then Brian is a lion. It is likely that if 'Greg is yellow' or 'Julius is a swan' or both then Sandra dropped the milk.
There is almost no chance that either 'Brian is a lion' or 'Sandra dropped the milk' but not both.
Chances are about even that either 'Brian is a lion' or 'Sandra dropped the milk' but not both.
There is almost no chance that either 'Brian is a lion' or 'Sandra dropped the milk' 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
  0.7::factA.
  1.0::factB.
  0.2::factC.
  %hop1
  0.9::factX:-and(factC,factA).
  0.1::factY:-or(factB,factC).
  0.7::factZ:-or(factC,factA).

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

  query(conclusion).
  
Either 'Brian is a lion' or 'Sandra dropped the milk' but not both.