It is highly likely that Jessica is a sheep. It is probably the case that Mary left the football. There is a better than even chance that Brian is white. Chances are about even that if 'Mary left the football' or 'Jessica is a sheep' or both then Gertrude is a mouse. It is certain that if 'Jessica is a sheep' or 'Brian is white' or both then Fred dropped the apple. It is improbable that if either 'Jessica is a sheep' or 'Brian is white' but not both then Julius is a swan.
There is a better than even chance that either 'Fred dropped the apple' or 'Jessica is a sheep' but not both.
It is highly unlikely that either 'Fred dropped the apple' or 'Jessica is a sheep' but not both.
There is a better than even chance that either 'Fred dropped the apple' or 'Jessica 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
  0.9::factA.
  0.7::factB.
  0.6::factC.
  %hop1
  0.5::factX:-or(factB,factA).
  1.0::factY:-or(factA,factC).
  0.1::factZ:-xor(factA,factC).

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

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