There is a very good chance that Winona is a mouse. It is certain that Julius is a frog. It is impossible that Greg is yellow. We doubt that if 'Greg is yellow' or 'Julius is a frog' or both then John dropped the milk. It is unlikely that if 'Julius is a frog and Winona is a mouse' then Bernhard is gray. There is a better than even chance that if 'Julius is a frog' or 'Greg is yellow' or both then Mary discarded the milk.
It is unlikely that either 'Winona is a mouse' or 'Greg is yellow' but not both.
There is a very good chance that either 'Winona is a mouse' or 'Greg is yellow' but not both.
It is unlikely that either 'Winona is a mouse' or 'Greg is yellow' 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
  0.8::factA.
  1.0::factB.
  0.0::factC.
  %hop1
  0.2::factX:-or(factC,factB).
  0.2::factY:-and(factB,factA).
  0.6::factZ:-or(factB,factC).

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

  query(conclusion).
  
Either 'Winona is a mouse' or 'Greg is yellow' but not both.