It is highly likely that Julius is a frog. It is certain that Brian is white. It is likely that John grabbed the apple. It is highly likely that if 'John grabbed the apple' or 'Julius is a frog' or both then Greg is yellow. It is highly likely that if 'Brian is white and Julius is a frog' then Bernhard is a swan. There is a very good chance that if 'Brian is white and Julius is a frog' then Mary is in the school.
It is probably the case that either 'Greg is yellow' or 'Julius is a frog' but not both.
We doubt that either 'Greg is yellow' or 'Julius is a frog' but not both.
It is probably the case that either 'Greg is yellow' or 'Julius 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
  0.9::factA.
  1.0::factB.
  0.7::factC.
  %hop1
  0.9::factX:-or(factC,factA).
  0.9::factY:-and(factB,factA).
  0.8::factZ:-and(factB,factA).

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

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