It is likely that Julius is a lion. It is unlikely that Mary moved to the office. It is likely that Greg is a swan. Chances are slight that if 'Julius is a lion' or 'Greg is a swan' or both then John went to the garden. It is highly unlikely that if 'Mary moved to the office and Greg is a swan' then Daniel left the milk. We believe that if either 'Mary moved to the office' or 'Greg is a swan' but not both then Bernhard is gray.
We doubt that 'Greg is a swan' or 'Bernhard is gray' or both.
We believe that 'Greg is a swan' or 'Bernhard is gray' or both.
We doubt that 'Greg is a swan' or 'Bernhard is gray' or 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.
  0.2::factB.
  0.7::factC.
  %hop1
  0.1::factX:-or(factA,factC).
  0.05::factY:-and(factB,factC).
  0.75::factZ:-xor(factB,factC).

  %hop2
  conclusion:-or(factC,factZ).

  query(conclusion).
  
'Greg is a swan' or 'Bernhard is gray' or both.