It is probably the case that Greg is a frog. We believe that Brian is a rhino. It is impossible that John put down the milk. There is almost no chance that if 'Brian is a rhino' or 'Greg is a frog' or both then Jessica is a cat. Chances are about even that if either 'John put down the milk' or 'Brian is a rhino' but not both then Mary grabbed the apple. We believe that if 'Brian is a rhino and John put down the milk' then Bernhard is a frog.
There is almost no chance that 'Brian is a rhino' or 'Greg is a frog' or both.
It is almost certain that 'Brian is a rhino' or 'Greg is a frog' or both.
There is almost no chance that 'Brian is a rhino' 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
  0.7::factA.
  0.75::factB.
  0.0::factC.
  %hop1
  0.02::factX:-or(factB,factA).
  0.5::factY:-xor(factC,factB).
  0.75::factZ:-and(factB,factC).

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

  query(conclusion).
  
'Brian is a rhino' or 'Greg is a frog' or both.