It is likely that Greg is a frog. It is highly likely that Lily is green. It is certain that Bernhard is gray. It is highly unlikely that if 'Greg is a frog' or 'Lily is green' or both then Antoine is hungry. It is highly likely that if 'Bernhard is gray' or 'Greg is a frog' or both then Julius is a swan. There is a very good chance that if either 'Lily is green' or 'Bernhard is gray' but not both then Mary dropped the milk.
There is almost no chance that either 'Julius is a swan' or 'Antoine is hungry' but not both.
It is highly likely that either 'Julius is a swan' or 'Antoine is hungry' but not both.
There is almost no chance that either 'Julius is a swan' or 'Antoine is hungry' 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
  0.7::factA.
  0.9::factB.
  1.0::factC.
  %hop1
  0.05::factX:-or(factA,factB).
  0.9::factY:-or(factC,factA).
  0.8::factZ:-xor(factB,factC).

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

  query(conclusion).
  
Either 'Julius is a swan' or 'Antoine is hungry' but not both.