There is a very good chance that Yann is bored. Chances are slight that Bernhard is a swan. It is highly likely that Sandra dropped the milk. It is probably the case that if 'Sandra dropped the milk' or 'Bernhard is a swan' or both then Julius is a lion. It is improbable that if either 'Bernhard is a swan' or 'Sandra dropped the milk' but not both then Lily is a frog. There is a very good chance that if 'Sandra dropped the milk and Bernhard is a swan' then Mary went to the garden.
It is impossible that 'Bernhard is a swan and Lily is a frog'.
It is impossible that 'Bernhard is a swan and Lily is a frog'.
There is a very good chance that 'Bernhard is a swan and Lily 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
  0.8::factA.
  0.1::factB.
  0.9::factC.
  %hop1
  0.7::factX:-or(factC,factB).
  0.1::factY:-xor(factB,factC).
  0.8::factZ:-and(factC,factB).

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

  query(conclusion).
  
'Bernhard is a swan and Lily is a frog'.