Chances are about even that Mary got the milk. It is certain that John went to the garden. It is probably not the case that Greg is white. There is almost no chance that if 'John went to the garden and Greg is white' then Lily is a rhino. It is highly unlikely that if 'Greg is white' or 'John went to the garden' or both then Gertrude is a sheep. We believe that if 'Mary got the milk' or 'Greg is white' or both then Bernhard is a frog.
There is a better than even chance that 'Mary got the milk' or 'Bernhard is a frog' or both.
There is a better than even chance that 'Mary got the milk' or 'Bernhard is a frog' or both.
It is impossible that 'Mary got the milk' or 'Bernhard 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
  0.5::factA.
  1.0::factB.
  0.25::factC.
  %hop1
  0.02::factX:-and(factB,factC).
  0.05::factY:-or(factC,factB).
  0.75::factZ:-or(factA,factC).

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

  query(conclusion).
  
'Mary got the milk' or 'Bernhard is a frog' or both.