We doubt that Sandra dropped the milk. It is impossible that Bill went to the kitchen. It is almost certain that Brian is a lion. It is certain that if 'Brian is a lion and Sandra dropped the milk' then Julius is white. It is probably the case that if 'Brian is a lion and Bill went to the kitchen' then Bernhard is a frog. We doubt that if either 'Bill went to the kitchen' or 'Sandra dropped the milk' but not both then Greg is a swan.
It is impossible that 'Bill went to the kitchen' or 'Bernhard is a frog' or both.
It is impossible that 'Bill went to the kitchen' or 'Bernhard is a frog' or both.
There is a better than even chance that 'Bill went to the kitchen' or 'Bernhard is a frog' 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
  0.2::factA.
  0.0::factB.
  0.95::factC.
  %hop1
  1.0::factX:-and(factC,factA).
  0.7::factY:-and(factC,factB).
  0.2::factZ:-xor(factB,factA).

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

  query(conclusion).
  
'Bill went to the kitchen' or 'Bernhard is a frog' or both.