It is probably not the case that Mary grabbed the milk. It is probable that Sandra dropped the milk. There is a better than even chance that John got the apple. There is almost no chance that if 'Sandra dropped the milk and John got the apple' then Bernhard is a frog. We doubt that if 'Mary grabbed the milk and John got the apple' then Lily is yellow. There is a better than even chance that if 'Sandra dropped the milk' or 'Mary grabbed the milk' or both then Julius is a swan.
There is little chance that 'Bernhard is a frog' or 'John got the apple' or both.
There is a better than even chance that 'Bernhard is a frog' or 'John got the apple' or both.
There is little chance that 'Bernhard is a frog' or 'John got the apple' 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
  0.25::factA.
  0.7::factB.
  0.6::factC.
  %hop1
  0.02::factX:-and(factB,factC).
  0.2::factY:-and(factA,factC).
  0.6::factZ:-or(factB,factA).

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

  query(conclusion).
  
'Bernhard is a frog' or 'John got the apple' or both.