We believe that Brian is gray. There is little chance that Bernhard is a frog. There is a very good chance that John went to the garden. It is unlikely that if 'Bernhard is a frog' or 'John went to the garden' or both then Julius is yellow. There is a better than even chance that if 'John went to the garden' or 'Brian is gray' or both then Mary dropped the milk. Chances are about even that if 'John went to the garden' or 'Brian is gray' or both then Lily is green.
It is highly unlikely that 'Brian is gray and Mary dropped the milk'.
Chances are about even that 'Brian is gray and Mary dropped the milk'.
It is highly unlikely that 'Brian is gray and Mary 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
  0.75::factA.
  0.1::factB.
  0.8::factC.
  %hop1
  0.2::factX:-or(factB,factC).
  0.6::factY:-or(factC,factA).
  0.5::factZ:-or(factC,factA).

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

  query(conclusion).
  
'Brian is gray and Mary dropped the milk'.