It is unlikely that John dropped the apple. It is certain that Gertrude is a cat. There is a very good chance that Winona is a mouse. There is almost no chance that if 'John dropped the apple' or 'Winona is a mouse' or both then Mary took the milk. It is impossible that if either 'Winona is a mouse' or 'John dropped the apple' but not both then Bernhard is a frog. It is probable that if either 'Winona is a mouse' or 'Gertrude is a cat' but not both then Brian is a rhino.
It is impossible that 'Bernhard is a frog and Mary took the milk'.
It is impossible that 'Bernhard is a frog and Mary took the milk'.
Chances are about even that 'Bernhard is a frog and Mary took 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.
  1.0::factB.
  0.8::factC.
  %hop1
  0.02::factX:-or(factA,factC).
  0.0::factY:-xor(factC,factA).
  0.7::factZ:-xor(factC,factB).

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

  query(conclusion).
  
'Bernhard is a frog and Mary took the milk'.