It is improbable that Julius is a swan. It is improbable that Bernhard is a frog. It is likely that Mary picked up the apple. Chances are about even that if either 'Julius is a swan' or 'Mary picked up the apple' but not both then Winona is a mouse. It is highly unlikely that if 'Mary picked up the apple' or 'Bernhard is a frog' or both then Greg is a swan. It is unlikely that if 'Julius is a swan' or 'Mary picked up the apple' or both then Brian is a lion.
It is highly unlikely that 'Mary picked up the apple and Bernhard is a frog'.
It is highly unlikely that 'Mary picked up the apple and Bernhard is a frog'.
There is a better than even chance that 'Mary picked up the apple and Bernhard is a frog'.

  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.
  0.1::factB.
  0.7::factC.
  %hop1
  0.5::factX:-xor(factA,factC).
  0.05::factY:-or(factC,factB).
  0.2::factZ:-or(factA,factC).

  %hop2
  conclusion:-and(factC,factB).

  query(conclusion).
  
'Mary picked up the apple and Bernhard is a frog'.