It is likely that Julius is a swan. Chances are slight that Bernhard is a frog. There is almost no chance that Yann is thirsty. Chances are about even that if either 'Bernhard is a frog' or 'Yann is thirsty' but not both then Brian is white. Chances are slight that if either 'Julius is a swan' or 'Yann is thirsty' but not both then John picked up the milk. It is unlikely that if 'Julius is a swan and Yann is thirsty' then Bill went to the kitchen.
There is almost no chance that 'Yann is thirsty and Julius is a swan'.
There is almost no chance that 'Yann is thirsty and Julius is a swan'.
It is certain that 'Yann is thirsty and Julius is a swan'.

  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.
  0.1::factB.
  0.02::factC.
  %hop1
  0.5::factX:-xor(factB,factC).
  0.1::factY:-xor(factA,factC).
  0.2::factZ:-and(factA,factC).

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

  query(conclusion).
  
'Yann is thirsty and Julius is a swan'.