It is highly likely that Bernhard is a frog. There is little chance that John dropped the apple. Chances are about even that Greg is a swan. It is highly unlikely that if 'John dropped the apple and Bernhard is a frog' then Mary grabbed the milk. We doubt that if 'John dropped the apple and Bernhard is a frog' then Bill moved to the office. We doubt that if 'Bernhard is a frog and Greg is a swan' then Brian is white.
There is almost no chance that 'John dropped the apple and Bill moved to the office'.
There is almost no chance that 'John dropped the apple and Bill moved to the office'.
There is a very good chance that 'John dropped the apple and Bill moved to the office'.

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

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

  query(conclusion).
  
'John dropped the apple and Bill moved to the office'.