There is a better than even chance that Winona is a sheep. It is likely that Mary dropped the apple. There is almost no chance that Brian is white. There is a very good chance that if 'Mary dropped the apple' or 'Brian is white' or both then Lily is a rhino. It is likely that if 'Winona is a sheep' or 'Mary dropped the apple' or both then Bill went to the kitchen. There is little chance that if 'Winona is a sheep' or 'Brian is white' or both then Greg is a lion.
It is highly unlikely that either 'Mary dropped the apple' or 'Winona is a sheep' but not both.
Chances are about even that either 'Mary dropped the apple' or 'Winona is a sheep' but not both.
It is highly unlikely that either 'Mary dropped the apple' or 'Winona is a sheep' 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.
  0.7::factB.
  0.02::factC.
  %hop1
  0.8::factX:-or(factB,factC).
  0.7::factY:-or(factA,factB).
  0.1::factZ:-or(factA,factC).

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

  query(conclusion).
  
Either 'Mary dropped the apple' or 'Winona is a sheep' but not both.