It is impossible that Bernhard is a swan. We believe that Julius is yellow. It is highly likely that Greg is a frog. It is almost certain that if either 'Julius is yellow' or 'Bernhard is a swan' but not both then John dropped the milk. There is little chance that if 'Bernhard is a swan' or 'Greg is a frog' or both then Mary moved to the office. Chances are about even that if 'Bernhard is a swan' or 'Julius is yellow' or both then Winona is a cat.
There is a very good chance that 'Mary moved to the office and Greg is a frog'.
It is improbable that 'Mary moved to the office and Greg is a frog'.
There is a very good chance that 'Mary moved to the office and Greg 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
  0.0::factA.
  0.75::factB.
  0.9::factC.
  %hop1
  0.95::factX:-xor(factB,factA).
  0.1::factY:-or(factA,factC).
  0.5::factZ:-or(factA,factB).

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

  query(conclusion).
  
'Mary moved to the office and Greg is a frog'.