We doubt that Jeff put down the milk. Chances are slight that Daniel dropped the apple. It is certain that Lily is a frog. It is certain that if 'Daniel dropped the apple' or 'Lily is a frog' or both then Greg is a swan. It is probably not the case that if either 'Lily is a frog' or 'Daniel dropped the apple' but not both then John went to the garden. There is a better than even chance that if either 'Jeff put down the milk' or 'Daniel dropped the apple' but not both then Bernhard is a lion.
It is certain that 'Jeff put down the milk' or 'Lily is a frog' or both.
It is certain that 'Jeff put down the milk' or 'Lily is a frog' or both.
It is impossible that 'Jeff put down the milk' or 'Lily is a frog' or both.

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

  %hop2
  conclusion:-or(factA,factC).

  query(conclusion).
  
'Jeff put down the milk' or 'Lily is a frog' or both.