It is almost certain that Brian is a frog. It is almost certain that Bernhard is a lion. Chances are slight that Greg is a frog. It is likely that if either 'Bernhard is a lion' or 'Greg is a frog' but not both then John dropped the apple. There is almost no chance that if 'Bernhard is a lion' or 'Brian is a frog' or both then Fred went to the office. There is a very good chance that if 'Bernhard is a lion' or 'Brian is a frog' or both then Sandra took the milk.
There is almost no chance that either 'Greg is a frog' or 'Brian is a frog' but not both.
It is highly likely that either 'Greg is a frog' or 'Brian is a frog' but not both.
There is almost no chance that either 'Greg is a frog' or 'Brian is a frog' 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
  0.95::factA.
  0.95::factB.
  0.1::factC.
  %hop1
  0.7::factX:-xor(factB,factC).
  0.02::factY:-or(factB,factA).
  0.8::factZ:-or(factB,factA).

  %hop2
  conclusion:-xor(factC,factA).

  query(conclusion).
  
Either 'Greg is a frog' or 'Brian is a frog' but not both.