There is almost no chance that John went to the office. There is almost no chance that Greg is a lion. There is little chance that Brian is white. Chances are about even that if 'John went to the office and Brian is white' then Bernhard is a rhino. It is improbable that if 'John went to the office and Brian is white' then Winona is a mouse. It is highly likely that if either 'John went to the office' or 'Brian is white' but not both then Julius is a frog.
There is little chance that either 'Julius is a frog' or 'Bernhard is a rhino' but not both.
There is little chance that either 'Julius is a frog' or 'Bernhard is a rhino' but not both.
There is a better than even chance that either 'Julius is a frog' or 'Bernhard is a rhino' but not 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
  0.02::factA.
  0.02::factB.
  0.1::factC.
  %hop1
  0.5::factX:-and(factA,factC).
  0.1::factY:-and(factA,factC).
  0.9::factZ:-xor(factA,factC).

  %hop2
  conclusion:-xor(factZ,factX).

  query(conclusion).
  
Either 'Julius is a frog' or 'Bernhard is a rhino' but not both.