It is impossible that Bernhard is a rhino. It is probably not the case that Brian is green. Chances are slight that Greg is a frog. It is probable that if 'Bernhard is a rhino' or 'Greg is a frog' or both then Lily is a swan. It is probably the case that if 'Greg is a frog and Brian is green' then Jessica is a sheep. It is probably the case that if 'Bernhard is a rhino' or 'Brian is green' or both then John put down the milk.
It is highly unlikely that either 'Lily is a swan' or 'Bernhard is a rhino' but not both.
It is highly unlikely that either 'Lily is a swan' or 'Bernhard is a rhino' but not both.
There is a very good chance that either 'Lily is a swan' or 'Bernhard is a rhino' 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
  0.0::factA.
  0.25::factB.
  0.1::factC.
  %hop1
  0.7::factX:-or(factA,factC).
  0.7::factY:-and(factC,factB).
  0.7::factZ:-or(factA,factB).

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

  query(conclusion).
  
Either 'Lily is a swan' or 'Bernhard is a rhino' but not both.