It is highly unlikely that Winona is a wolf. It is improbable that Greg is yellow. It is unlikely that Lily is gray. There is almost no chance that if 'Winona is a wolf' or 'Lily is gray' or both then Gertrude is a sheep. It is highly likely that if 'Lily is gray and Winona is a wolf' then Sandra left the milk. It is probably the case that if 'Winona is a wolf' or 'Greg is yellow' or both then Brian is a frog.
There is little chance that either 'Greg is yellow' or 'Winona is a wolf' but not both.
There is little chance that either 'Greg is yellow' or 'Winona is a wolf' but not both.
It is almost certain that either 'Greg is yellow' or 'Winona is a wolf' 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
  0.05::factA.
  0.1::factB.
  0.2::factC.
  %hop1
  0.02::factX:-or(factA,factC).
  0.9::factY:-and(factC,factA).
  0.7::factZ:-or(factA,factB).

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

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