It is highly unlikely that Mary grabbed the milk. We doubt that Fred dropped the apple. We believe that Lily is a lion. It is unlikely that if either 'Mary grabbed the milk' or 'Fred dropped the apple' but not both then Greg is a swan. It is probably the case that if 'Mary grabbed the milk' or 'Lily is a lion' or both then Bernhard is a frog. It is probable that if either 'Fred dropped the apple' or 'Lily is a lion' but not both then Brian is green.
It is highly unlikely that 'Lily is a lion and Mary grabbed the milk'.
It is highly unlikely that 'Lily is a lion and Mary grabbed the milk'.
There is a better than even chance that 'Lily is a lion and Mary grabbed 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
  0.05::factA.
  0.2::factB.
  0.75::factC.
  %hop1
  0.2::factX:-xor(factA,factB).
  0.7::factY:-or(factA,factC).
  0.7::factZ:-xor(factB,factC).

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

  query(conclusion).
  
'Lily is a lion and Mary grabbed the milk'.