There is a better than even chance that Bernhard is gray. There is little chance that Julius is green. Chances are slight that Greg is a frog. It is unlikely that if either 'Julius is green' or 'Greg is a frog' but not both then Gertrude is a cat. There is little chance that if either 'Greg is a frog' or 'Bernhard is gray' but not both then Sandra dropped the apple. It is highly unlikely that if 'Greg is a frog' or 'Julius is green' or both then Bill left the football.
It is certain that either 'Julius is green' or 'Gertrude is a cat' but not both.
There is little chance that either 'Julius is green' or 'Gertrude is a cat' but not both.
It is certain that either 'Julius is green' or 'Gertrude is a cat' 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
  0.6::factA.
  0.1::factB.
  0.1::factC.
  %hop1
  0.2::factX:-xor(factB,factC).
  0.1::factY:-xor(factC,factA).
  0.05::factZ:-or(factC,factB).

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

  query(conclusion).
  
Either 'Julius is green' or 'Gertrude is a cat' but not both.