It is highly likely that Julius is a rhino. It is probably the case that Greg is a frog. It is unlikely that Mary dropped the milk. It is unlikely that if either 'Mary dropped the milk' or 'Julius is a rhino' but not both then John left the football. It is highly likely that if 'Greg is a frog and Mary dropped the milk' then Bernhard is a frog. There is little chance that if either 'Mary dropped the milk' or 'Greg is a frog' but not both then Emily is a wolf.
There is a better than even chance that either 'Greg is a frog' or 'John left the football' but not both.
There is a better than even chance that either 'Greg is a frog' or 'John left the football' but not both.
Chances are slight that either 'Greg is a frog' or 'John left the football' 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
  0.9::factA.
  0.7::factB.
  0.2::factC.
  %hop1
  0.2::factX:-xor(factC,factA).
  0.9::factY:-and(factB,factC).
  0.1::factZ:-xor(factC,factB).

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

  query(conclusion).
  
Either 'Greg is a frog' or 'John left the football' but not both.