It is certain that Gertrude is a mouse. It is improbable that Sandra left the milk. It is probably not the case that Greg is white. Chances are slight that if 'Greg is white' or 'Sandra left the milk' or both then John went to the garden. There is a better than even chance that if 'Gertrude is a mouse and Greg is white' then Brian is a swan. We doubt that if 'Greg is white and Gertrude is a mouse' then Mary dropped the milk.
There is a very good chance that 'Gertrude is a mouse and John went to the garden'.
There is almost no chance that 'Gertrude is a mouse and John went to the garden'.
There is a very good chance that 'Gertrude is a mouse and John went to the garden'.

  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
  1.0::factA.
  0.1::factB.
  0.25::factC.
  %hop1
  0.1::factX:-or(factC,factB).
  0.6::factY:-and(factA,factC).
  0.2::factZ:-and(factC,factA).

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

  query(conclusion).
  
'Gertrude is a mouse and John went to the garden'.