We doubt that Sandra dropped the milk. It is probable that Jason is tired. There is a very good chance that Julius is gray. We doubt that if either 'Julius is gray' or 'Jason is tired' but not both then Bernhard is a frog. There is little chance that if 'Jason is tired' or 'Julius is gray' or both then John went to the kitchen. It is improbable that if 'Jason is tired and Julius is gray' then Brian is a rhino.
There is almost no chance that 'Bernhard is a frog and Sandra dropped the milk'.
There is almost no chance that 'Bernhard is a frog and Sandra dropped the milk'.
It is highly likely that 'Bernhard is a frog and Sandra dropped the milk'.

  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.
  0.7::factB.
  0.8::factC.
  %hop1
  0.2::factX:-xor(factC,factB).
  0.1::factY:-or(factB,factC).
  0.1::factZ:-and(factB,factC).

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

  query(conclusion).
  
'Bernhard is a frog and Sandra dropped the milk'.