It is unlikely that Daniel left the milk. It is unlikely that Julius is a frog. Chances are about even that John dropped the apple. Chances are slight that if either 'John dropped the apple' or 'Julius is a frog' but not both then Greg is white. We doubt that if either 'Julius is a frog' or 'Daniel left the milk' but not both then Brian is a rhino. There is almost no chance that if 'John dropped the apple' or 'Julius is a frog' or both then Mary moved to the garden.
There is almost no chance that 'Brian is a rhino' or 'John dropped the apple' or both.
Chances are about even that 'Brian is a rhino' or 'John dropped the apple' or both.
There is almost no chance that 'Brian is a rhino' or 'John dropped 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
  0.2::factA.
  0.2::factB.
  0.5::factC.
  %hop1
  0.1::factX:-xor(factC,factB).
  0.2::factY:-xor(factB,factA).
  0.02::factZ:-or(factC,factB).

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

  query(conclusion).
  
'Brian is a rhino' or 'John dropped the apple' or both.