We doubt that John went to the hallway. Chances are about even that Jeff dropped the apple. We believe that Greg is a frog. It is probably the case that if 'Greg is a frog' or 'John went to the hallway' or both then Mary took the milk. It is impossible that if 'Jeff dropped the apple' or 'John went to the hallway' or both then Brian is a rhino. It is impossible that if 'Greg is a frog' or 'John went to the hallway' or both then Julius is gray.
It is improbable that 'Mary took the milk' or 'Greg is a frog' or both.
There is a very good chance that 'Mary took the milk' or 'Greg is a frog' or both.
It is improbable that 'Mary took the milk' or 'Greg 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.
  0.5::factB.
  0.75::factC.
  %hop1
  0.7::factX:-or(factC,factA).
  0.0::factY:-or(factB,factA).
  0.0::factZ:-or(factC,factA).

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

  query(conclusion).
  
'Mary took the milk' or 'Greg is a frog' or both.